How to Setup SPI Master (AVR ASM)
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;**** A P P L I C A T I O N N O T E A V R 3 2 0 ***************** ;* ;* Title : Software SPI Master ;* Version : 1.0 ;* Last updated : 98.04.21 ;* Target : AT90S1200 ;* Easily modified for : Any AVR microcontroller ;* ;* Support E-mail :avr@atmel.com ;* ;* DESCRIPTION ;* This is a collection of 8/16-bit word, Mode 0, Master SPI routines. ;* It simultaneously transmits and receives SPI data in 8- or 16-bit ;* word format. Data is sent and received MSB-first. One pair of ;* registers is used both to send and to receive; i.e., when one bit ;* is shifted out (transmitted), the vacated bit position is used to ;* store the new received bit. These routines are low-level ;* interface routines, and do not inherently contain a command ;* structure; that is dictated by the connected SPI peripheral(s). ;* ;* Due to having separate Enable/Disable and Read/Write-Word ;* routines, larger blocks of data can be sent simply by calling ;* the RW_SPI routine multiple times before disabling /SS. ;* ;* MAJOR ROUTINES: ;* init_spi: initializes the port lines used for SPI. ;* No calling requirements, returns nothing. ;* ena_spi: forces SCK low, and activates /SS signal. ;* No calling requirements, returns nothing. ;* disa_spi: brings /SS signal hi (inactive). ;* No calling requirements, returns nothing. ;* rw_spi: sends/receives a an 8-bit or 16-bit data word. ;* Must set up data to be sent in (spi_hi,spi_lo) ;* prior to calling; it returns received data in ;* the same register pair (if 8-bit, uses only ;* the spi_lo register). ;* ;* VARIABLES: ;* The spi_hi and spi_lo variables are the high and low data bytes. ;* They can be located anywhere in the register file. ;* ;* The temp variable holds the bit count, and is also used in timing ;* the high/low minimum pulse width. This must be located in an ;* upper register due to the use of an IMMEDIATE-mode instruction. ;* ;* HISTORY ;* V1.0 98.04.21 (rgf) Created ;* ;*************************************************************************** ;**** includes **** .include "1200def.inc" ;you can change this to any device ;*************************************************************************** ;* ;* CONSTANTS ;* ;*************************************************************************** ;**** Revision Codes **** .equ SW_MAJOR = 1 ; Major SW revision number .equ SW_MINOR = 0 ; Minor SW revision number .equ HW_MAJOR = 0 ; Major HW revision number .equ HW_MINOR = 0 ; Minor HW revision number ;*************************************************************************** ;* ;* PORT DEFINITIONS ;* ;*************************************************************************** .equ sck = 0 ;PB0 pin .equ nss = 1 ;PB1 pin .equ mosi = 2 ;PB2 pin .equ miso = 3 ;PB3 pin ;*************************************************************************** ;* ;* REGISTER DEFINITIONS ;* ;*************************************************************************** .def spi_lo =r0;change as needed .def spi_hi =r1; " .def temp =r16;misc usage, must be in upper regs for IMMED mode ;*************************************************************************** ;* ;* MACROS ;* Program Macros ;* ;* DESCRIPTION ;* Change the following macros if a port other than PORTB is used. ;* ;*************************************************************************** .macro ss_active cbi portb,nss .endm .macro ss_inactive sbi portb,nss .endm .macro sck_hi sbi portb,sck .endm .macro sck_lo cbi portb,sck .endm .macro mosi_hi sbi portb,mosi .endm .macro mosi_lo cbi portb,mosi .endm .macro addi subi @0, -@1 ;subtract the negative of an immediate value .endm .macro set_delay ;set up the time delay amount, from 1 to 7 subi @0, (@1 << 5);NOTE: THIS shift affects INC macro (below)! .endm .macro inc_delay ;bump the delay counter subi @0, -(1 << 5);shift value here must be same as above! .endm ;*************************************************************************** ;* ;* SAMPLE APPLICATION, READY TO RUN ON AN AT90S1200 ;* ;*************************************************************************** .cseg .org 0 Rvect: rjmp Reset ;*************************************************************************** ;* ;* FUNCTION ;* init_spi ;* ;* DESCRIPTION ;* Initialize our port pins for use as SPI master. ;* ;* CODE SIZE: ;* 8 words ;* ;*************************************************************************** init_spi: ss_inactive ;set latch bit hi (inactive) sbi ddrb,nss;make it an output ; sck_lo ;set clk line lo sbi ddrb,sck;make it an output ; mosi_lo ;set data-out lo sbi ddrb,mosi;make it an output ; cbi ddrb,miso;not really required, it powers up clr'd! ret ;*************************************************************************** ;* ;* FUNCTION ;* ena_spi ;* ;* DESCRIPTION ;* Init data & clock lines, then assert /SS. Note that if more than ;* one slave is used, copies of this could be made that would each ;* reference a different /SS port pin (use SS_ACTIVE0, SS_ACTIVE1, ...) ;* ;* CODE SIZE: ;* 4 words ;* ;*************************************************************************** ena_spi: sck_lo ;(should already be there...) mosi_lo ss_active ret ;*************************************************************************** ;* ;* FUNCTION ;* disa_spi ;* ;* DESCRIPTION ;* De-assert /SS. Since this routine is so short, it might be better ;* to use the SS_INACTIVE statement directly in higher level code. ;* Again, if multiple slaves exist, additional copies of this could ;* be created; or ONE routine that disabled ALL /ss signals could be ;* used instead to make the code less error-prone due to calling the ;* wrong Disable routine. ;* ;* CODE SIZE: ;* 2 words ;* ;*************************************************************************** disa_spi: ss_inactive ret ;*************************************************************************** ;* ;* FUNCTION ;* rw_spi ;* ;* DESCRIPTION ;* Write a word out on SPI while simultaneously reading in a word. ;* Data is sent MSB-first, and info read from SPI goes into ;* the same buffer that the write data is going out from. ;* Make sure data, clock and /SS are init'd before coming here. ;* SCK high time is ((delay * 3) + 1) AVR clock cycles. ;* ;* If 8-bit use is needed, change LDI TEMP,16 to ,8 and also ;* eliminate the ROL SPI_HI statement. ;* ;* CODE SIZE: ;* 21 words ;* NUMBER OF CYCLES: ;* Overhead = 8, loop = 16 * (16 + (2* (delay_value*3))) ; (With call + return + delay=4, it is about 648 cycles.) ;* ;*************************************************************************** rw_spi: ldi temp,16 ;init loop counter to 16 bits ;ldi temp,8 ;use THIS line instead if 8-bit desired ; spi_loop: lsl spi_lo ;move 0 into D0, all other bits UP one slot, rol spi_hi ; and C ends up being first bit to be sent. ;If 8-bit desired, also comment out the preceding ROL SPI_HI statement ; brcc lo_mosi mosi_hi rjmp mosi_done;this branch creates setup time on MOSI lo_mosi: mosi_lo nop ;also create setup time on MOSI mosi_done: ; sck_hi ; ;must now time the hi pulse - not much else we can do here but waste time ; set_delay temp,4;(4 * 3) cycle delay; range is from 1 to 7! time_hi: inc_delay temp ;inc upper nibble until it rolls over; then, brcs time_hi ; C gets CLEARED, & temp has original value ; sck_lo ;drop clock line low ; ;must now delay before reading in SPI data on MISO ; set_delay temp,4 time_lo: inc_delay temp brcs time_lo ; sbic pinb,miso;after delay, read in SPI bit & put into D0 inc spi_lo ;we FORCED D0=0, so use INC to set D0. ; dec temp brne spi_loop ret ;************************ End of SPI routines **************************** ;**** Application example **** Reset: rcall init_spi ser temp ;load w/ FF out DDRD,temp rjmp Main Main: ldi R22,0xA3;misc data mov spi_lo,R22;set up information to be sent mov spi_hi,R22;COMMENT THIS OUT IF 8-BIT MODE rcall ena_spi ;activate /SS rcall rw_spi ;send/receive 16 bits (or 8 bits) rcall disa_spi;deactivate /SS rcall use_spi_rcv;go use whatever we received rjmp Main Use_spi_rcv: ;just copy rcv'd data to Port D pins out PortD,R22 ret ;**** End of File **** |