注：本文是作者以前發表在其個人博客，現在發布到電子發燒友專欄

本例是用針對標準I2C接口EEPROM存儲器24C02進行讀寫操作，只要對例程做適當修改，就可以用到大部分控制I2C接口設備的場合。

應廣單片機軟件I2C接口例程（MASTER模式）

本例僅供參考，歡迎指正程序中的問題

//-----------------------------------------
.chip p201cs14a
//{{PADAUK_CODE_OPTION
.Code_OptionBootupSlow// 1024 ILRC
.Code_OptionLVD2.79V// Maximum performance = 4 MIPS
.Code_OptionSecurityEnable// Security 3/4 words Enable
//}}PADAUK_CODE_OPTION

//定義I2C接口
I2C_SDAequpa.7
I2C_SCLequpa.6
I2C_SDA_DIRequpac.7
I2C_SCL_DIRequpac.6
I2C_LONG_DLYequ50
I2C_SHORT_DLYequ20
I2C_SDA_HIGHequset1I2C_SDA
I2C_SDA_LOWequset0I2C_SDA
I2C_SCL_HIGHequset1I2C_SCL
I2C_SCL_LOWequset0I2C_SCL
I2C_SDA_OUTPUTequset1I2C_SDA_DIR
I2C_SDA_INPUTequset0I2C_SDA_DIR
I2C_SCL_OUTPUTequset1I2C_SCL_DIR
I2C_SCL_INPUTequset0I2C_SCL_DIR

//定義I2C變量
bytei2c_rw_addr//讀寫地址
bytei2c_rw_byte//讀寫數據
bytei2c_rw_cmd//讀寫的器件地址
bytei2c_rw_temp//讀寫過程中間變量
bytei2c_rw_cnt//讀寫過程中間變量

//
byteXms
bytems_cnt

//
bytetest_addr
bytetest_data

.romadr0x000
gotomain0
gotomain1

.romadr0x010
isr_entry:
pushaf
intrq = 0
popaf
reti

//----------------------------
//產生START信號
//----------------------------
i2c_start:
I2C_SDA_OUTPUT
I2C_SCL_OUTPUT
I2C_SDA_HIGH
delayI2C_LONG_DLY
I2C_SCL_HIGH
delayI2C_LONG_DLY
I2C_SDA_LOW
delayI2C_LONG_DLY
I2C_SCL_LOW
delayI2C_LONG_DLY
ret

//----------------------------
//產生STOP信號
//----------------------------
i2c_stop:
I2C_SCL_LOW
delayI2C_LONG_DLY
I2C_SDA_LOW
delayI2C_LONG_DLY
I2C_SCL_HIGH
delayI2C_LONG_DLY
I2C_SDA_HIGH
delayI2C_LONG_DLY
//
I2C_SCL_INPUT
I2C_SDA_INPUT
ret

//----------------------------
//檢查SALVE ACK信號
//----------------------------
i2c_slave_ack:
//don't check ACK
I2C_SDA_INPUT
delayI2C_SHORT_DLY
I2C_SCL_HIGH
delayI2C_SHORT_DLY
I2C_SCL_LOW
delayI2C_SHORT_DLY
I2C_SDA_OUTPUT
I2C_SDA_LOW
delayI2C_SHORT_DLY
ret

//----------------------------
//輸出MASTER ACK信號
//----------------------------
i2c_master_ack:
I2C_SDA_OUTPUT
I2C_SDA_LOW
delayI2C_SHORT_DLY
I2C_SCL_HIGH
delayI2C_SHORT_DLY
I2C_SCL_LOW
delayI2C_SHORT_DLY
ret

//----------------------------
//輸出MASTER NACK信號
//----------------------------
i2c_master_nack:
I2C_SDA_OUTPUT
I2C_SDA_HIGH
delayI2C_SHORT_DLY
I2C_SCL_HIGH
delayI2C_SHORT_DLY
I2C_SCL_LOW
delayI2C_SHORT_DLY
ret

//------------------------------
//寫一個字節
//Input: i2c_rw_temp
//Used: i2c_rw_cnt
//------------------------------
i2c_write_8bit:
i2c_rw_cnt = 8
i2c_write_8bit_loop:
slci2c_rw_temp
swapcI2C_SDA
delayI2C_SHORT_DLY
I2C_SCL_HIGH
delayI2C_SHORT_DLY
I2C_SCL_LOW
delayI2C_SHORT_DLY
dzsni2c_rw_cnt
gotoi2c_write_8bit_loop
ret

//------------------------------
//讀一個字節
//Used: i2c_rw_cnt
//Output: i2c_rw_temp
//------------------------------
i2c_read_8bit:
i2c_rw_temp = 0
i2c_rw_cnt = 8
delayI2C_SHORT_DLY
i2c_read_8bit_loop:
I2C_SCL_HIGH
delayI2C_SHORT_DLY
swapcI2C_SDA
slci2c_rw_temp
I2C_SCL_LOW
delayI2C_SHORT_DLY
dzsni2c_rw_cnt
gotoi2c_read_8bit_loop
ret

//------------------------------
//Input: i2c_rw_addr
// i2c_rw_cmd
//Used: i2c_rw_cnt
// i2c_rw_temp
//Output: i2c_rw_byte
//------------------------------
i2c_read_byte:
//start
calli2c_start

//write device address(write)
i2c_rw_temp = i2c_rw_cmd
calli2c_write_8bit

//slave ack
calli2c_slave_ack

//write register address
i2c_rw_temp = i2c_rw_addr
calli2c_write_8bit

//slave ack
//don't check ACK
calli2c_slave_ack

//start repeat
calli2c_start

//write device address(read)
i2c_rw_temp = i2c_rw_cmd
i2c_rw_temp.0 = 1
calli2c_write_8bit

//slave ack
//don't check ACK
I2C_SDA_INPUT
delayI2C_SHORT_DLY
I2C_SCL_HIGH
delayI2C_SHORT_DLY
I2C_SCL_LOW
delayI2C_SHORT_DLY//這里為特殊情況I2C_SDA不用轉為輸出

//read data
i2c_rw_temp = 0
calli2c_read_8bit
i2c_rw_byte = i2c_rw_temp//store data

//master nack
calli2c_master_nack

//stop
calli2c_stop

//retune
delayI2C_LONG_DLY
wdreset
ret

//------------------------------
//Input: i2c_rw_addr
// i2c_rw_byte
// i2c_rw_cmd
//Used: i2c_rw_cnt
// i2c_rw_temp
//------------------------------
i2c_write_byte:
//start
calli2c_start

//write device address
i2c_rw_temp = i2c_rw_cmd
calli2c_write_8bit

//slave ack
//don't check ACK
calli2c_slave_ack

//write register address
i2c_rw_temp = i2c_rw_addr
calli2c_write_8bit

//slave ack
//don't check ACK
calli2c_slave_ack

//write data
i2c_rw_temp = i2c_rw_byte
calli2c_write_8bit

//slave ack
//don't check ACK
calli2c_slave_ack

//stop
calli2c_stop

//retune
delayI2C_LONG_DLY
wdreset
ret

EEPROM_RW_CMDequ0xA0
//------------------------------
//函數名: eeprom_read_byte
//Input: i2c_rw_addr
//Used: i2c_rw_cnt
// i2c_rw_temp
//Output: i2c_rw_byte
//------------------------------
eeprom_read_byte:
i2c_rw_cmd = EEPROM_RW_CMD
gotoi2c_read_byte//注意這里用的是跳轉
//------------------------------
//函數名: eeprom_write_byte
//Input: i2c_rw_addr
// i2c_rw_byte
//Used: i2c_rw_cnt
// i2c_rw_temp
//注意： 調用完后需要等待一段時間以保證寫操作完成
//------------------------------
eeprom_write_byte:
i2c_rw_cmd = EEPROM_RW_CMD
gotoi2c_write_byte//注意這里用的是跳轉

//----------------------------------------
//input: ms
//該函數以4M頻率為基準時鐘實現延時
//----------------------------------------
delayXms:
while(Xms)
{
wdreset
ms_cnt = 20
while(ms_cnt)
{
delay195
ms_cnt--
}
Xms--
}
ret

main0:
.ADJUST_OTP_IHRCR8MIPS// IHRC/2 = 8MIPS, WatchDog Disable, RAM 0,1 temporary be used
sp = 0x30

disgint
inten = 0

pa = 0b0000_0000
paph = 0b1101_0000
pac = 0b0000_0001
pb = 0b0000_0000
pbph = 0b0000_0000
pbc = 0b1111_1111

I2C_SDA_INPUT
I2C_SCL_INPUT

delay200

mova,0b100_11_111
movt16m,a

clkmd.1 = 1//enable watch dog
wdreset

Xms = 100
calldelayXms

test_data = 0
test_addr = 0

main0_loop:
wdreset

//寫E2EPROM
i2c_rw_addr = test_addr
i2c_rw_byte = test_data
calleeprom_write_byte

//調用EEPROM寫操作函數后要等待一段時間，以保證數據寫操作完成
Xms = 20
calldelayXms

//讀E2EPROM
i2c_rw_addr = test_addr
calleeprom_read_byte
if(i2c_rw_byte != test_data)
{
//讀回的數據比較出錯，判斷為讀寫E2PROM出錯
nop
}

test_addr ++
test_data --

gotomain0_loop

//----------------FPPA1-------------------
main1:
sp = 52
main1_loop:
gotomain1_loop

本例代碼是從實際程序中移植而來，已編譯，未做最終調試