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 AN131
Application Note
Interfacing the CS5521/22/23/24/28 to the 68HC05
TABLE OF CONTENTS
1. INTRODUCTION ................................................... 1 2. ADC DIGITAL INTERFACE ................................... 1 3. SOFTWARE DESCRIPTION ................................. 2 3.1 Initialize ............................................................. 2 3.2 Write Channel Setup Registers ........................ 2 3.3 Self-Offset Calibration ....................................... 3 3.4 Read/Write Gain Register ................................. 3 3.5 Acquiring Conversions ...................................... 4 4. MAXIMUM SCLK RATE ......................................... 4 5. CONCLUSION ....................................................... 5 6. APPENDIX: 68HC05 MICROCODE TO INTERFACE TO THE CS5521/22/23/24/28 ................................ 6
2. ADC DIGITAL INTERFACE
The CS5521/22/23/24/28 interfaces to the 68HC05 through either a three-wire or a four-wire interface. Figure 1 depicts the interface between the two devices. Though this software was written to interface to the three-wire SPITM on the 68HC05, the algorithms can be easily modified to work in the four-wire format. The ADC's serial port consists of four control lines: CS, SCLK, SDI, and SDO. CS, Chip Select, is the control line which enables access to the serial port. SCLK, Serial Clock, is the bit-clock which controls the shifting of data to or from the ADC's serial port. SDI, Serial Data In, is the data signal used to transfer data from the 68HC05 to the ADC. SDO, Serial Data Out, is the data signal used to transfer output data from the ADC to the 68HC05.
1. INTRODUCTION
This application note details the interface of Cirrus Logic's Crystal(R) CS5521/22/23/24/28 Analog-toDigital Converter (ADC) to a Motorola 68HC05 microcontroller. This note takes the reader through a simple example describing how to communicate with the ADC. All algorithms discussed are included in Section 6. "APPENDIX: 68HC05 Microcode to Interface to the CS5521/22/23/24/28" on page 6.
3-Wire Interface CS5521/22/23/24/28 CS SDI SDO SCLK 68HC05 No Connect MOSI (PD3) MISO (PD2) SCK (PD4)
4-Wire Interface CS5521/22/23/24/28 CS SDI SDO SCLK 68HC05 PA0 MOSI (PD3) MISO (PD2) SCK (PD4)
Figure 1. 3-Wire and 4-Wire Interfaces
P.O. Box 17847, Austin, Texas 78760 (512) 445 7222 FAX: (512) 445 7581 http://www.cirrus.com
Copyright (c) Cirrus Logic, Inc. 1999 (All Rights Reserved)
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3. SOFTWARE DESCRIPTION
This note presents algorithms to initialize the 68HC05 and the CS5521/22/23/24/28, modify the CS5521/22/23/24/28's internal registers, perform calibrations, and acquire conversions. Figure 2 depicts a block diagram of the program structure. While reading this application note, please refer to Section 6. "APPENDIX: 68HC05 Microcode to Interface to the CS5521/22/23/24/28" on page 6 for the code listing. purposes only). This is implemented by sending the converter fifteen bytes of logic 1's followed by one final byte, with its LSB at logic 0. This sequence places the serial port of the ADC into the command state, where it waits for a valid command.
3.2 Write Channel Setup Registers
The subroutine write_csrs is an example of how to write to the CS5521/22/23/24/28's Channel Setup Registers (CSRs). For this example, two CSRs (four Setups) are written. The number of CSRs to be accessed is determined by the Depth Pointer bits (DP3-DP0) in the configuration register. The Depth Pointer bits are set to "0011" to access the two CSRs. The value "0011" is calculated by takSTART
3.1 Initialize
Initialize is a subroutine that configures the SPI on the 68HC05 and places the CS5521/22/23/24/28 into the command state. The SPI is configured as depicted in Figure 1 by selecting the 68HC05 as the master. To function properly with the CS5521/22/23/24/28, the SPI must be set up to use a clock which idles low, and begins clocking data with a rising edge in the center of the first bit (for more information on configuring the SPI refer to Motorola's 68HC05 Application Guide). After configuring the SPI, the controller enters a delay state to allow time for the CS5521/22/23/24/28's power-on-reset and oscillator to start-up (oscillator start-up time for a 32.768 KHz crystal is typically 500 ms). The last step is to reinitialize the serial port on the ADC (reinitializing the serial port is unnecessary here, and the code is for demonstration
INITIALIZE MICROCONTROLLER AND CS5521/22/23/24/28
SELF-OFFSET CAL.
MODIFY GAIN
ACQUIRE CONVERSION
Figure 2. CS5521/22/23/24/28 Software Flowchart
Contacting Cirrus Logic Support
For a complete listing of Direct Sales, Distributor, and Sales Representative contacts, visit the Cirrus Logic web site at: http://www.cirrus.com/corporate/contacts/
SPITM is a trademark of Motorola. MicrowireTM is a trademark of National Semiconductor. Preliminary product information describes products which are in production, but for which full characterization data is not yet available. Advance product information describes products which are in development and subject to development changes. Cirrus Logic, Inc. has made best efforts to ensure that the information contained in this document is accurate and reliable. However, the information is subject to change without notice and is provided "AS IS" without warranty of any kind (express or implied). No responsibility is assumed by Cirrus Logic, Inc. for the use of this information, nor for infringements of patents or other rights of third parties. This document is the property of Cirrus Logic, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. No part of this publication may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc. Items from any Cirrus Logic website or disk may be printed for use by the user. However, no part of the printout or electronic files may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc.Furthermore, no part of this publication may be used as a basis for manufacture or sale of any items without the prior written consent of Cirrus Logic, Inc. The names of products of Cirrus Logic, Inc. or other vendors and suppliers appearing in this document may be trademarks or service marks of their respective owners which may be registered in some jurisdictions. A list of Cirrus Logic, Inc. trademarks and service marks can be found at http://www.cirrus.com.
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ing the number of Setups to be accessed and subtracting 1. Because each CSR holds two Setups, this number must always be an odd value, that is, DP0 must always be logic 1 when reading and writing the CSRs. To modify the Depth Pointer bits, the configuration register is read to prevent corruption of other bits. After the read_register routine is run with the command 0x0B (HEX), the DP3-DP0 bits are masked to "0011". Then, the updated information is written back into the ADC with the command 0x03 (HEX) using the write_register routine. After the depth pointer bits are set correctly, the CSR information is written to the ADC. The command 0x05 (HEX) is sent to the ADC to begin the write sequence (to read the CSRs, the command would be 0x0D). At this point, the ADC is expecting to receive information for two 24-bit CSRs, or 48 bits, based on the Depth Pointer bits. The first CSR is written with a value of 0x000000 (HEX). This sets Setup 1 and Setup 2 both to convert bipolar, 100mV signals on physical channel 1 (PC1) at an output word rate (OWR) of 15 Hz, and latch pins A1-A0 equal to "00". The second CSR is written with the value 0x4C0105 (HEX). This sets Setup 3 to convert a bipolar, 100mV signal on PC2 at a 101.1 Hz OWR, with latch pins A1-A0 at "01". This also sets Setup 4 to convert a unipolar, 25mV input signal at 15 Hz on PC3, with output latch pins A1-A0 set to "00". Setup, the offset or gain register that is modified belongs to the physical channel referenced by that Setup.
3.4 Read/Write Gain Register
The routine rwgain provides an example of how to modify the ADC's internal gain registers. To modify the gain register the command byte and data byte variables are written with the appropriate information. rwgain then calls the subroutine write_register, which uses these variables to set the contents of Physical Channel 1 (PC1)'s gain register to 0x800000 (HEX). The write_register routine calls the send_spi algorithm four times, once to send the command byte, and three more times to send the three data bytes. Send_spi is a subroutine which transfers data to the CS5521/22/23/24/28 MSB-first through the SPI. Figure 3 depicts the timing diagram for the write-cycle in the CS5521/22/23/24/28's serial port. It is important to note here that this section of the code demonstrates how to write to the gain register of PC1. It does not perform a gain calibration. To write to the other internal registers of the ADC, follow the procedures outlined in the CS5522/24/28 and CS5521/23 data sheets. To read the value in the gain register of PC1, the command byte is loaded with the value 0x0A (HEX), and the read_register routine is called. It duplicates the read-cycle timing diagram depicted in Figure 4. Read_register calls send_spi once to transfer the command-byte to the CS5521/22/23/24/28. This places the converter into the data state where it waits until data is read from its serial port. Read_register then calls receive_spi three times and transfers three bytes of information from the CS5521/22/23/24/28 to the 68HC05. Similar to send_spi, receive_spi acquires a byte one bit at a time, MSB-first from the SPI. When the transfer is complete, the variables high_byte, mid_byte, and low_byte contain the value present in PC1's 24-bit gain register.
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3.3 Self-Offset Calibration
Calibrate is a subroutine that performs a self-offset calibration using Setup 1. Calibrate does this by sending the command 0x81 (HEX) to the ADC through the SPI. This tells the ADC to perform a self-offset calibration using Setup 1 (see the CS5522/24/28 and CS5521/23 Data Sheets for information on performing offset or gain calibrations using other Setups). Once the command has been sent, the controller polls MISO (SDO) until it falls, indicating that the calibration is complete. Note that although calibrations are done using a specific
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3.5 Acquiring Conversions
To acquire a conversion the subroutine convert is called. For single conversions on one physical channel, the MC (multiple conversion) and the LP (loop) bits in the configuration register must be logic 0. To prevent corruption of the configuration register, convert instructs the 68HC05 to read and save the contents. This information is stored in the variables HIGHBYTE, MIDBYTE and LOWBYTE. Then the MC, LP, and RC (read convert) bits are masked to logic 0, and the new information is written back to the ADC's configuration register. A conversion is initiated using Setup 1 by sending the command 0x80 to the converter. At this time, the controller polls MOSI (SDO) until it falls to a logic 0 level (see Figure 5). After SDO falls, convert calls send_spi to send one byte of all 0's to the converter to clear the SDO flag. The 68HC05 then reads the conversion data word by calling receive_spi three times. Figure 6 depicts how the 16 and 24-bit data words are stored in the memory locations HIGHBYTE, MIDBYTE, and LOWBYTE.
4. MAXIMUM SCLK RATE
A machine cycle in the 68HC05 consists of 2 oscillator periods or 500 ns if the microcontroller's oscillator frequency is 4 MHz. Since the CS5521/22/23/24/28's maximum SCLK rate is 2 MHz, additional no operation (NOP) delays may be necessary to reduce the transfer rate if the microcontroller system requires higher rate oscillators.
Figure 3. Write-Cycle Timing
Figure 4. Read-Cycle Timing
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SCLK
SDI
Command Time 8 SCLKs
SDO
td *
XIN/OWR Clock Cycles 8 SCLKs Clear SDO Flag
MSB
LSB
* td = XIN/OWR clock cycles for each conversion except the first conversion which will take XIN/OWR + 7 clock cycles
Data Time 24 SCLKs
Data SDO Continuous Conversion Read
Figure 5. Conversion/Acquisition Cycle Timing
5. CONCLUSION
MSB D23 High-Byte D22 D21 D20 D19 D18 D17 D16 Mid-Byte D15 D14 D13 D12 D11 D10 D9 D8 Low-Byte D7 D6 D5 D4 D3 D2 D1 D0 A) 24-Bit Conversion Data Word (CS5522/24/28) High-Byte D12 D11 D10 D9 D8 Mid-Byte D7 D6 D5 D4 D3 D2 D1 D0 Low-Byte 1 1 1 0 CI1 CI0 OD OF B) 16-Bit Conversion Data Word (CS5521/23) D14 D13 0- always zero, 1- always one, CI1, CI0 - Channel Indicator Bits OD - Oscillation Detect, OF - Overflow Figure 6. Bit Representation/Storage in 68HC05
MSB D15
This application note presents an example of how to interface the CS5521/22/23/24/28 to the 68HC05. It is divided into two main sections: hardware and software. The hardware interface illustrates both three-wire and a four-wire interface. The three-wire interface is SPI and MicrowireTM compatible. The software section illustrates how to initialize the converter and microcontroller, write to the CSRs, write and read the ADC's internal registers, perform calibrations, and acquire conversions. The software is modularized and provides important subroutines such as write_register, read_register, write_csrs and convert, which were all written in 68HC05 assembly language. The software described in the note is included in Section 6. "APPENDIX: 68HC05 Microcode to Interface to the CS5521/22/23/24/28" on page 6.
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6. APPENDIX: 68HC05 MICROCODE TO INTERFACE TO THE CS5521/22/23/24/28
;***************************************************************************** ;* File: 55226805.ASM ;* Date: September 23, 1998 ;* Revision:0 ;* Processor:68HC05 ;* ;* Program entry point at routine 'main'. Entry point address is $100 ;* ;* This program is an example on how to interface a 68HC05 Microcontroller ;* to a CS5521/22/23/24/28 ADC. The program interfaces via the SPI port (Port D) ;* on the microcontroller, which controls the serial communications, ;* calibration, and conversion cycles. ;*****************************************************************************
;*** Memory Map Equates *** PORTA DDRA PORTD SPCR SPSR SPDR SPIF ;*** RAM Values *** ORG HIGHBYTE MIDBYTE LOWBYTE COMMAND RMB RMB RMB RMB $50 1 1 1 1 ;Upper 8 bits of Conversion Register ;Middle 8 bits of Conversion Register ;Lower 8 bits of Conversion Register ;Command Byte storage location EQU EQU EQU EQU EQU EQU EQU $00 $04 $03 $0A $0B $0C 7 ;General Purpose I/O Port ;Data Direction Control for Port A ;Port D Direct Pin Access (Input) ;Serial Peripheral Control Register ;Serial Peripheral Status Register ;Serial Peripheral Data I/O Register ;Serial Peripheral Data Transfer Flag
;***************************************************************************** ;* Program Code ;***************************************************************************** ORG $100
;***************************************************************************** ;* Routine - main ;* Input - none ;* Output - none ;* This is the entry point and the main loop of the program. ;*****************************************************************************
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MAIN
EQU
*
;Start from reset vector
;*** Initialize and Calibrate the system *** JSR initialize JSR JSR JSR write_csrs calibrate rwgain
;Initialize the System ;Modify the Channel Setup Registers ;Calibrate ADC Offset ;Write and read gain register
;*** Continuously perform single conversions *** mloop: JSR convert JMP mloop ;*** End MAIN ***
;Obtain a conversion from the ADC ;Keep Looping
;***************************************************************************** ;* Subroutines ;***************************************************************************** ;***************************************************************************** ;* Routine - initialize ;* Input - none ;* Output - none ;* This subroutine initializes Port D as a SPI port to interface to the ;* CS5521/22/23/24/28 ADC. ;* A time delay for the ADC oscillator start-up period is provided, as well ;* as a delay for the ADC's power-on reset. ;* Typically, a 32.768 KHz crystal has a start-up time of about 500ms. After ;* this delay, an additional 1003 XIN cycles are delayed for the ADC reset. ;* The ADC's serial port is also reset at this time ;***************************************************************************** initialize LDA #%01010000 STA LDA JSR LDA JSR JSR JSR ;Load ACCA with values for SPCR SPCR ;Setup SPI Port #$40 ;Load ACCA with delay count value delay ;Delay 1003 XIN for power-on reset #220 ;Load ACCA with delay count value delay ;Delay for oscillator start-up 170ms delay ;Delay for oscillator start-up 170ms delay ;Delay for oscillator start-up 170ms
sloop:
;*** Initialize ADC serial port *** LDX LDA JSR DECX
#$0F #$FF send_spi
;Value of 15 for first 15 Bytes ;Load ACCA with all 1's ;Send info to ADC ;Decrement Counter
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BNE LDA JSR RTS sloop #%11111110 send_spi ;Repeat loop if counter isn't zero ;Load ACCA with last byte ;Send final byte to ADC ;Exit routine
;***************************************************************************** ;* Routine - write_csrs ;* Input - none ;* Output - none ;* This subroutine is used to write to the Channel Setup Registers. It first ;* changes the depth pointer bits in the configuration register to reflect ;* the number of CSRs to be written, and then writes information to the ;* appropriate number of CSRs. ;***************************************************************************** write_csrs LDA #$0B STA JSR ;Command to read config. register COMMAND ;Prepare command byte read_register;Read the configuration register
;*** Mask DP3-DP0 to access two CSRS (four Setups) *** LDA MIDBYTE ;Get Middle Byte in ACCA AND #$3F ;Mask DP3-DP2 low ORA #$30 ;Mask DP1-DP0 high STA MIDBYTE ;Put info back into Middle Byte location LDA #$03 ;Command to write back to config Register STA COMMAND ;Prepare Command Byte JSR write_register;Write Configuration Register ;*** Write to CSRs - note, the ADC expects information for the number of ; CSRs indicated in the Depth Bits (DP3-DP0 in the configuration ; register) so all of the CSRs must be written at this time. LDA JSR #$05 send_spi ;Command to write CSRs ;send command to ADC
;*** Setup CSR #1 - Setups 1 and 2 ; Sets both Setups to a default value of '000' ; (A1-A0 = 00, Physical Channel = 1, OWR = 15Hz, ; Input V-range = 100mV, Bipolar Measurement Mode) LDA JSR JSR JSR #$00 send_spi send_spi send_spi ;Load ACCA with zeros ;One byte of zero... ;Two bytes of zero... ;Three bytes of zero.
;*** Setup CSR #2 - Setups 3 and 4 ; Sets Setup 3 to '4C0' and Setup 4 to '105' ; Setup 3 Settings - (A1-A0 = 01, Physical Channel = 2, OWR = 101.1Hz, ; input V-range = 100mV, Bipolar)
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; ; Setup 4 Settings - (A1-A0 = 00, Physical Channel = 3, OWR = 15Hz, input V-range = 25mV, Unipolar) LDA JSR LDA JSR LDA JSR RTS #$4C send_spi #$01 send_spi #$05 send_spi ;Load ACCA with first byte of CSR #2 ;Send byte number one ;Load ACCA with second byte of CSR #2 ;Send byte number two ;Load ACCA with third byte of CSR #2 ;Send byte number three ;Exit subroutine
;***************************************************************************** ;* Routine - calibrate ;* Input - none ;* Output - none ;* This subroutine instructs the CS5521/22/23/24/28 to perform a self-calibration on ;* Setup 1. ;***************************************************************************** calibrate poll_sdo1 LDA JSR BRSET RTS #$81 send_spi 2,PORTD, poll_sdo1 ;Command for Self-Offset Cal, Setup 1 ;Send Self-Cal command to ADC ;Wait for SDO to fall ;Exit Routine
;***************************************************************************** ;* Routine - rwgain ;* Input - none ;* Output - contents of gain register on PC1 in HIGH, MID and LOW bytes ;* This subroutine first writes, and then reads back the value of the gain ;* register on Physical Channel 1 ;***************************************************************************** ;*** Write to Gain Register of Physical Channel 1 *** LDA #$02 ;Command to Write Gain Register of PC 1 STA COMMAND ;Prepeare COMMAND byte LDA #$80 ;Value for High Byte STA HIGHBYTE ;Prepare HIGHBYTE CLR MIDBYTE ;Prepare MIDBYTE CLR LOWBYTE ;Prepare LOWBYTE JSR write_register;Write to Gain Register ;*** Read From Gain Register of Physical Channel 1 *** LDA #$0A ;Command to Read Gain Register of PC 1 STA COMMAND ;Prepare COMMAND byte JSR read_register;Read from Gain Register RTS ;Return
rwgain
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;***************************************************************************** ;* Routine - convert ;* Input - none ;* Output - conversion results in memory locations HIGHBYTE, MIDBYTE and ;* LOWBYTE. This algorithm performs single conversions on ;* Setup 1. See the CS5521/22/23/24/28 data sheet for multiple ;* conversions or conversions on other channels. ;* This subroutine performs a Single conversion using Setup 1 ;***************************************************************************** convert LDA STA JSR LDA AND STA LDA STA JSR #$0B ;Command to read Configuration Register COMMAND ;Prepare COMMAND byte read_register;Read Config. Register HIGHBYTE ;Get High Byte in ACCA #$F8 ;Mask MC, LP and RC bits to 0 HIGHBYTE ;Put info back into High Byte location #$03 ;Command to write back to config Register COMMAND ;Prepare Command Byte write_register;Write Configuration Register
;*** Receive Conversion Data *** LDA JSR poll_sdo2: BRSET LDA JSR JSR STA JSR STA JSR STA RTS
#$80 send_spi 2,PORTD,poll_sdo2 #$00 send_spi receive_spi HIGHBYTE receive_spi MIDBYTE receive_spi LOWBYTE
;Command to convert on Setup 1 ;Send Command to ADC ;Wait for SDO to fall ;Load A with all 0's ;Send all 0's to ADC ;Get high conversion byte ;Move info to High Byte location ;Get middle conversion byte ;Move info to Middle Byte location ;Get low conversion byte ;Move info to Low Byte location ;Return
;***************************************************************************** ;* Routine - write_register ;* Input - COMMAND, HIGHBYTE, MIDBYTE, LOWBYTE ;* Output - none ;* This subroutine is used to write information to the internal registers of ;* the CS5521/22/23/24/28 ;***************************************************************************** write_register LDA JSR LDA JSR LDA JSR LDA COMMAND send_spi HIGHBYTE send_spi MIDBYTE send_spi LOWBYTE ;Load ACCA with COMMAND ;Transfer command byte ;Load ACCA with HIGHBYTE ;Transfer high byte ;Load ACCA with MIDBYTE ;Transfer middle byte ;Load ACCA with LOWBYTE
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JSR RTS send_spi ;Transfer low byte ;Return
;***************************************************************************** ;* Routine - read_register ;* Input - COMMAND ;* Output - HIGHBYTE, MIDBYTE, LOWBYTE ;* This subroutine is used to read from the internal registers of the ;* CS5521/22/23/24/28 ;***************************************************************************** read_register LDA JSR JSR STA JSR STA JSR STA RTS COMMAND send_spi receive_spi HIGHBYTE receive_spi MIDBYTE receive_spi LOWBYTE ;Load ACCA with COMMAND ;Send command byte ;Receive a byte ;Store value in HIGHBYTE ;Receive a byte ;Store value in MIDBYTE ;Receive a byte ;Store value in LOWBYTE ;Return
;***************************************************************************** ;* Routine - send_spi ;* Input - Byte to be send is placed in ACCA ;* Output - none ;* This subroutine sends a byte to the ADC using the SPI port. ;***************************************************************************** send_spi wait0: STA BRCLR RTS SPDR SPIF,SPSR,wait0 ;Move ACCA to the SPI Data Register ;Loop until byte has been transmitted ;Return
;***************************************************************************** ;* Routine - receive_spi ;* Input - none ;* Output - Received byte is placed in ACCA ;* This subroutine receives a byte from the ADC using the SPI port ;***************************************************************************** receive_spi wait1: CLRA STA BRCLR LDA RTS ;Load ACCA Register with all Zeros ;Transfer 8 0's to clock next byte ;Reset SPIF bit ;Get received information ;Return
SPDR SPIF,SPSR,wait1 SPDR
;*****************************************************************************
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;* Routine - delay ;* Input - count in ACCA ;* Output - none ;* This routine delays by using the count specified in ACCA. The 68HC05 ;* Development Board uses a 4.0MHz clock (E = 2.0MHz), thus each cycle is ;* 500ns. This delay is equivalent to (500ns)*(1545)(count value) ;* A count of 720 provides a 556ms delay. ;***************************************************************************** delay outlp: innlp: NOP CLRX DECX NOP NOP BNE DECA BNE RTS
innlp outlp
;X used as inner loop count ;256 loops on inner ;2 cycles ;2 cycles ;10 cycles*256*500ns=1.28ms ;countdown accumulator ;2569 cycles*500ns*ACCA ;Return
;***************************************************************************** ;* Interrupt Vectors ;***************************************************************************** NOT_USEDRTI ORG FDB FDB FDB FDB FDB FDB $1FF4 NOT_USED NOT_USED NOT_USED NOT_USED NOT_USED MAIN ;Return from interrupt ;Int Vector location ;SPI interrupt ;SPI interrupt ;SPI interrupt ;SPI interrupt ;SPI interrupt ;Reset interrupt - power on reset
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* Notes *


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