;**************************************************************************** ;* The following code enhanced MCS-51-BASIC with four commands for I2C ;* communication as bus master and can be an example for creating custom ;* statements for MCS-51-BASIC. The four statements and the syntax to use ;* are: ;* ;* I2CSTART Sends a start condition to I2C bus. ;* - Returns with busy, time out or status clear. ;* I2CSTOP Sends a stop condition to I2C bus. ;* - Returns with time out or status clear. ;* I2CPUT [byte] Sends a byte to the I2C bus. ;* - Returns with time out, no acknowledge or clear. ;* I2CGET [variable] Reads a byte from I2C to a BASIC variable. ;* - Set 180H (status) to 1 to send no acknowledge: ;* DBY(18H) = 1 : I2CGET B : I2CSTOP : PRINT B ;* - Returns with time out or status clear. ;* ;* Register 18H is the I2C communication status register; useage is: ;* ;* STATUS=DBY(18H) ;* IF STATUS.AND.2=2 PRINT "Time out error!" ;* IF STATUS.AND.4=4 PRINT "Busy error!" ;* IF STATUS.AND.8=8 PRINT "No acknowlege error!" ;* ;* (C) H.-J. Boehling 09.15.99 ;* www.germany.net/teilnehmer/101.107378 ;* www.isis.de/members/~boehling ;* ;**************************************************************************** ;----- Definitions ---------------------------------------------------------- SDA equ P1.6 ;I2C serial data line. SCL equ P1.5 ;I2C serial clock line. status equ 018H ;Communication status. ; the following bits will be set in the status byte: tout equ 00000010B ;I2C time out status. busy equ 00000100B ;I2C bus busy status. nack equ 00001000B ;Slave sends no acknowledge. value2var equ 0A80H ;Address of MCS-51-BASIC ;routine to give a value on ;argument stack to a variable. ;---------------------------------------------------------------------------- ; The following code is necessary to notify the new statements to BASIC. org 2002H ;5Ah at 2002h tells BASIC-52 db 5AH ;to call 2048h (see below). org 2048H ;Set bit 45 to tell BASIC-52 ;that custom commands or setb 45 ;instructions have been ret ;added. org 2070H ;Store starting address of mov dptr,#vectortable ;vector table. ret org 2078H ;Store starting address of mov dptr,#tokentable ;token table. ret vectortable: ;Vector table starts here. ;Label to branch on: dw i2cstart ;I2CSTART command dw i2cstop ;I2CSTOP command dw i2cput ;I2CPUT command dw i2cget ;I2CGET command tokentable: ;Token table starts here. db 10H ;1. user defined token for db "I2CSTART" ;command name. db 0 ;End of token indicator db 11H ;2. user defined token for db "I2CSTOP" ;command name. db 0 ;End of token indicator. db 12H ;3. user defined token for db "I2CPUT" ;command name. db 0 ;End of token indicator. db 13H ;4. user defined token for db "I2CGET" ;command name. db 0FFH ;End of list indicator. ;---------------------------------------------------------------------------- ; Here starts the code for the new BASIC statements. org 3000h ;use any available address ;===== i2cstart - sends an I2C start condition to beginn communication ====== i2cstart: call SCLhigh ;Set SCL to high. mov R7,#4 ;Load time out counter. setSDA: setb SDA ;Set SDA to high. jb SDA,ishigh ;If not high bus is busy. djnz R7,setSDA ;If not try until R7 is zero. orl status,#busy ;Set busy status. ret ;return to BASIC. ishigh: clr SDA ;Set start condition. anl status,#0 ;Clear I2C status. ret ;return to BASIC. ;===== i2cstop - sends an I2C stop condition to end communication =========== i2cstop: anl status,#0 ;Clear I2C status. clr SDA ;Get SDA ready for stop. acall SCLhigh ;Set clock for stop. acall delay ;Delay 4 machine cycles. setb SDA ;Set stop condition. ret ;Return to BASIC. ;===== i2cput - sends a byte from a BASIC value out to the I2C bus ========== ;----- Get value and test for 8 bit only ------------------------------------ i2cput: mov A,#39H ;Put value to send on lcall 30H ;argument stack. mov A,#1 ;change value to 16 bit lcall 30H ;integer and write to R3:R1 cjne R3,#0,error ;If R3 not zero then ;value bigger than 0FFH. ;8 bit integer only error. ;----- Send byte to I2C bus ------------------------------------------------- mov A,R1 ;Load byte to send. mov R6,#8 ;Load bit counter send: clr SCL ;Make clock low acall delay ;Delay 4 machine cycles. rlc A ;Rotate data bit to C. mov SDA,C ;Put data bit on pin. acall SCLhigh ;Send clock. acall delay ;Delay 4 machine cycles. djnz R6,send ;Repeat until all bits sent. ;----- Read acknowledge from slave ------------------------------------------ clr SCL ;Make clock low. acall delay ;Delay 4 machine cycles. setb SDA ;Release line for acknowledge. acall SCLhigh ;Send clock for acknowlege. acall delay ;Delay 4 machine cycles. jnb SDA,ackok ;Check for valid acknowledge. orl status,#nack ;Set no acknowledge status. ackok: clr SCL ;Finish acknowledge bit. ret ;Return to BASIC. ;===== i2cget - Reads one byte from I2C bus to the argument stack =========== i2cget: mov R6,#8 ;Load bit counter read: clr SCL ;Make clock low. acall delay ;Delay 4 machine cycles. acall SCLhigh ;Send clock. acall delay ;Delay 4 machine cycles. mov C,SDA ;Get data bit from pin. rlc A ;Rotate bit into result byte. djnz R6,read ;Repeat until all received. ;----- Put received byte on argument stack ---------------------------------- mov R0,A ;Load R0 with reseived byte. mov R2,#0 ;Set high byte to zero. mov A,#9AH ;Put byte on argument stack lcall 30H ;with BASIC funktion. ;----- Send acknowledge to slave -------------------------------------------- clr SCL ;Set clock low. acall delay ;Delay 4 machine cycles. mov A,status ;Load acknowledge bit rrc A ;into C and mov SDA,C ;send acknowledge bit. acall SCLhigh ;Send acknowledge clock. ljmp value2var ;Set next variable to value ;on argument stack and ;return to BASIC. ;----- delay - generates a delay of 4 machine cycles ------------------------ ; (This routine is tuned for a oscilator frequency of 12MHz). delay: ret ;4 cycles for CALL and RET. ;----- SCLhigh - sends SCL pin high and waits for any clock stretching ------ SCLhigh: mov R7,#4 ;Load time out counter. setSCL: setb SCL ;Set SCL to high. jb SCL,quit ;If SCL actually high return. djnz R7,setSCL ;If not try until R7 is zero. orl status,#tout ;Set status time out. quit: ret ;----- error - sends an error message to the terminal ----------------------- error: mov A,#7 ;Send CR/LF lcall 30H mov R3,#high errmsg ;Set string address. mov R1,#low errmsg setb 34H ;Read string from code memory. mov A,#6 ;Send String to lcall 30H ;terminal. clr A ljmp 30H ;Back to command mode. errmsg: db "ERROR: BAD I2CPUT ARGUMENT" db 22H ;End of text. end