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i2c.asm
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; This file is part of Programator.
;
; Programator is free software: you can redistribute it and/or
; modify it under the terms of the GNU General Public License as
; published by the Free Software Foundation, either version 3 of the
; License, or (at your option) any later version.
;
; Programator is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with Programator. If not, see <https://www.gnu.org/licenses/>.
;
; Copyright (c) 2006, 2018, 2022 Aleksander Mazur
;
; Obsługa I2C / Two-Wire w trybie MASTER
; na podstawie "Interfacing AT24CXX Serial EEPROMs with AT89CX051 MCU" firmy Atmel
;-----------------------------------------------------------
; Opóźnienie adekwatne do szybkości działania I2C
i2c_delay macro
nop
endm
;-----------------------------------------------------------
; START na I2C
; zwraca C=1 jeśli wystąpił błąd
; niszczy A, C
i2c_start:
; Send START, defined as high-to-low SDA with SCL high.
; Return with SCL, SDA low.
; Returns CY set if bus is not available.
setb SCL
setb SDA
; Verify bus available.
jnb SCL, i2c_error ; jump if not high
jb SDA, i2c_start_cont
; After an interruption in protocol, power loss or system reset, any
; 2-wire part can be reset by following these steps:
; 1. Clock up to 9 cycles.
; 2. Look for SDA high in each cycle while SCL is high.
; 3. Create a start condition.
;push ACC
mov A, #9 ; bit count
i2c_reset_loop:
clr SCL ; drop clock
i2c_delay ; enforce SCL low and data setup
setb SCL ; raise clock
i2c_delay ; enforce SCL high
jb SDA, i2c_start_cont_pop
djnz ACC, i2c_reset_loop ; next bit
;pop ACC
i2c_error:
setb C ; set error flag
ret
i2c_start_cont_pop:
;pop ACC
i2c_start_cont:
clr C ; clear error flag
i2c_delay ; enforce setup delay and cycle delay
clr SDA
i2c_delay ; enforce hold delay
i2c_clr_SCL_ret:
clr SCL
ret
;-----------------------------------------------------------
; Odbiera bajt z I2C do akumulatora
; niszczy A, C, R6
i2c_shin:
; Shift in a byte from the AT24Cxx, most significant bit first.
; SCL expected low on entry. Return with SCL low.
; Returns received data byte in A.
setb SDA ; make SDA an input
mov R6, #8 ; bit count
i2c_shin_bit:
i2c_delay ; enforce SCL low and data setup
setb SCL ; raise clock
i2c_delay ; enforce SCL high
mov C, SDA ; input bit
rlc A ; move bit into byte
clr SCL ; drop clock
djnz R6, i2c_shin_bit ; next bit
ret
;-----------------------------------------------------------
; Wysyła bajt z akumulatora na I2C
; Niszczy A, C, R6
; Zwraca C=1 w razie błędu, C=0 po sukcesie
i2c_shout:
; Shift out a byte to the AT24Cxx, most significant bit first.
; SCL, SDA expected low on entry. Return with SCL low.
; Called with data to send in A.
; Returns CY set to indicate failure by slave to acknowledge.
; Destroys A.
mov R6, #8 ; bit counter
i2c_shout_bit:
rlc A ; move bit into CY
mov SDA, C ; output bit
i2c_delay ; enforce SCL low and data setup
setb SCL ; raise clock
i2c_delay ; enforce SCL high
clr SCL ; drop clock
djnz R6, i2c_shout_bit ; next bit
setb SDA ; release SDA for ACK
i2c_delay ; enforce SCL low and tAA
setb SCL ; raise ACK clock
i2c_delay ; enforce SCL high
mov C, SDA ; get ACK bit
sjmp i2c_clr_SCL_ret ; drop ACK clock
;-----------------------------------------------------------
; ACK na I2C
i2c_ACK:
; Clock out an acknowledge bit (low).
; SCL expected low on entry. Return with SCL, SDA low.
clr SDA ; ACK bit
i2c_delay ; enforce SCL low and data setup
setb SCL ; raise clock
i2c_delay ; enforce SCL high
sjmp i2c_clr_SCL_ret ; drop clock
;-----------------------------------------------------------
; NAK na I2C
i2c_NAK:
; Clock out a negative acknowledge bit (high).
; SCL expected low on entry. Return with SCL low, SDA high.
setb SDA ; NAK bit
i2c_delay ; enforce SCL low and data setup
setb SCL ; raise clock
i2c_delay ; enforce SCL high
sjmp i2c_clr_SCL_ret ; drop clock
;-----------------------------------------------------------
; STOP na I2C
i2c_stop:
; Send STOP, defined as low-to-high SDA with SCL high.
; SCL expected low on entry. Return with SCL, SDA high.
clr SDA
i2c_delay ; enforce SCL low and data setup
setb SCL
i2c_delay ; enforce setup delay
setb SDA
ret