Estoy intentando implementar SPI en el software para ATtiny45 (que no tiene soporte para SPI de forma nativa). Para probar uno estoy usando el potenciómetro digital, MCP4151 . Se conecta de la siguiente manera:
Microchipproporciona
;**** 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 :[email protected]
;*
;* 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 ; clear bit #nss in IO register #portb
.endm
.macro ss_inactive
sbi portb,nss ; set bit #nss in IO register #portb
.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 <=> temp = 16
;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 (carry bit) ends up being first bit to be sent.
; If 8-bit desired, also comment out the preceding ROL SPI_HI statement
;
brcc lo_mosi ; if C (carry bit) is clear - goto lo_mosi
mosi_hi ; else - goto 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 ****
Al leer la hoja de datos de MCP4151 , he implementado este programa para controlar el limpiaparabrisas de un potenciómetro digital:
#include <avr/io.h>
#include <util/delay.h>
#define F_CPU 16000000UL
#define CS PB1
#define SCK PB2
#define MOSI PB0
void SPIMasterInit() {
// set CS, SCK and MOSI to output
DDRB = (1 << CS) | (1 << SCK) | (1 << MOSI);
}
int SPITransmitData(unsigned char data) {
// SPI has two modes - 0,0 and 1,1 determined by the state of the SCK bit
// at the moment when CS goes from inactive (HIGH) to active (LOW)
// enable SPI mode 0,0:
// 1. set SCK to LOW
// 2. clear the MOSI output
// 3. set CS bit to LOW (select slave device)
PORTB &= ~((1 << SCK) | (1 << MOSI) | (1 << CS));
int received = 0;
for (int i = 0; i < 8; ++i) {
/* ====== writing stage ======== */
// first - send some data
// if the least significant bit of data is 1 - then set MOSI pin to HIGH, otherwise - set it to LOW
// here i'm using the bitwise AND operator, since it is way faster than the modulo 2
// most significant bit should go first!
if (data & (1 << 7)) {
PORTB |= (1 << MOSI);
} else {
PORTB &= ~(1 << MOSI);
}
// only after the data is about to be sent, send SCK
// this will determine SPI mode: 1,1 or 0,0
// set SCK to LOW
PORTB |= (1 << SCK);
// here we need to wait a little bit for slave to send us some data back
_delay_ms(1);
// shut down the SCK signal
PORTB &= ~(1 << SCK);
/* ====== reading stage ======== */
// turn MOSI into MISO!
DDRB &= ~(1 << MOSI);
// shift zero into the received
// this is effectively the same as data * 2
received <<= 1;
_delay_ms(1);
if (PINB & (1 << MOSI)) {
++received;
}
// roll that stuff back
DDRB |= (1 << MOSI);
// shift data one bit
// this is effectively the same as data * 2
data <<= 1;
}
// disable the slave device
PORTB |= (1 << CS);
// return what we have received
return received;
}
/**
* 16-bit commands:
* - write data: AAAA00ZD DDDDDDDD
* - read data: AAAA11ZX XXXXXXXX
*
* 8-bit commands:
* - increment (wiper position): AAAA01ZX
* - decrement (wiper position): AAAA10ZX
*
* here:
* - A - address bit
* - D - data bit, from master (MCU) to slave (digipot)
* - X - data bit, from slave (digipot) to master (MCU)
* - Z - error bit, LOW when an error occurs
*
* addresses:
* - 0x00 - default register
*/
int digipotWriteData(unsigned char data) {
SPITransmitData(0b00000000);
return SPITransmitData(data);
}
int digipotIncrement() {
return SPITransmitData(0b00000100);
}
int digipotDecrement() {
return SPITransmitData(0b00001000);
}
void main() {
SPIMasterInit();
digipotWriteData(0);
_delay_ms(2000);
while (1) {
digipotWriteData(0);
_delay_ms(2000);
digipotWriteData(64);
_delay_ms(2000);
digipotWriteData(128);
_delay_ms(2000);
digipotWriteData(192);
_delay_ms(2000);
digipotWriteData(255);
_delay_ms(2000);
}
}
El protocolo de comunicación de MCP4151 es bastante sencillo: hay cuatro comandos principales, a saber, lectura / escritura de datos en la memoria del dispositivo (efectivamente: obtener / establecer la posición del limpiador, cuando se trata del registro predeterminado 00h ) y aumentar / Disminuir la posición del limpiaparabrisas. El formato como lo entiendo lo he descrito en el comentario en el código fuente:
16-bit commands:
- write data: AAAA00ZD DDDDDDDD
- read data: AAAA11ZX XXXXXXXX
*
8-bit commands:
- increment (wiper position): AAAA01ZX
- decrement (wiper position): AAAA10ZX
*
here:
- A - address bit
- D - data bit, from master (MCU) to slave (digipot)
- X - data bit, from slave (digipot) to master (MCU)
- Z - error bit, LOW when an error occurs
*
addresses:
- 0x00 - default register
Por lo tanto, por ejemplo, para establecer la posición del limpiador en el medio de una escalera de resistencia, envío estos dos mensajes de 8 bits a IC:
0000 00 00 1000 0000
^^^^ ^^ ^^ ^^^^ ^^^^
default command extra data bits
register' bits data (wiper
address (write) bits position)
Y dado que el modo SPI 0,0 supone que MSB (bit más significativo) va primero a la salida, los bits se envían en este orden al IC:
0 0 0 0 0 0 0 0 1 0 0 0 0 0 0
time ----->
(como si normalmente leyeras el número decimal - de izquierda a derecha)
He hecho un prototipo en una placa de pruebas, conectando un multímetro para medir la resistencia del potenciómetro digital:
(por lo tanto, puse los retrasos de 2000 ms entre las escrituras de datos para evitar el retraso de medición del multímetro)
También conecté tres leds a través de las resistencias 330 Ohm entre los pines del potenciómetro digital ( SCK , CS y SDI/SDO ) y tierra para posiblemente depurar (ya que no tengo el osciloscopio). los datos se envían desde el maestro (MCU) al esclavo ( MCP4151 ), junto con el aumento de los retrasos en la función SPITransmitData() a aproximadamente 500 ms .
Puedo ver claramente que los bits se envían en el orden correcto (desde el bit más significativo hasta el bit menos significativo) al esclavo y la señal CS se está configurando correctamente, desde HIGH a LOW antes de la Transmisión de datos y hacia atrás después de la transmisión. Pero el potenciómetro no cambia su posición de limpiaparabrisas y su resistencia tampoco cambia.
La pregunta es bastante estándar: ¿qué estoy haciendo mal?