参数资料
型号: MC68HC05SB7
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDSO28
封装: MO-150, SSOP-28
文件页数: 162/170页
文件大小: 2161K
代理商: MC68HC05SB7
August 27, 1998
GENERAL RELEASE SPECIFICATION
MC68HC05SB7
SM-BUS
MOTOROLA
REV 2.1
12-13
ISR
BCLR
1,SMSR
; CLEAR THE SMIF FLAG
BRCLR
5,SMCR,SLAVE
; CHECK THE SMSTA FLAG,
; BRANCH IF SLAVE MODE
BRCLR
4,SMCR,RECEIVE
; CHECK THE MODE FLAG,
; BRANCH IF IN RECEIVE MODE
BRSET
0,SMSR,END
; CHECK ACK FROM RECEIVER
; IF NO ACK, END OF
; TRANSMISSION
TRANSMIT
LDA
DATABUF
; GET THE NEXT BYTE OF DATA
STA
SMDR
; TRANSMIT THE DATA
12.6.4 Generation of the STOP Signal
A data transfer ends with a STOP signal generated by the “master” device. A mas-
ter transmitter can simply generate a STOP signal after all the data has been
transmitted. The following is an example showing how a stop condition is gener-
ated by a master transmitter:
MASTX
BRSET
0,SMSR,END
; IF NO ACK, BRANCH TO END
LDA
TXCNT
; GET VALUE FROM THE
; TRANSMITTING COUNTER
BEQ
END
; IF NO MORE DATA, BRANCH TO
; END
LDA
DATABUF
; GET NEXT BYTE OF DATA
STA
SMDR
; TRANSMIT THE DATA
DEC
TXCNT
; DECREASE THE TXCNT
BRA
EMASTX
; EXIT
END
BCLR
5,SMCR
; GENERATE A STOP CONDITION
EMASTX
RTI
; RETURN FROM INTERRUPT
If a master receiver wants to terminate a data transfer, it must inform the slave
transmitter by not acknowledging the last byte of data. This can be done by setting
the transmit acknowledge bit (TXAK) before reading the 2nd last byte of data.
Before reading the last byte of data, a STOP signal must be generated rst. The
following is an example showing how a STOP signal is generated by a master
receiver.
MASR
DEC
RXCNT
BEQ
ENMASR
; LAST BYTE TO BE READ
LDA
RXCNT
DECA
; CHECK LAST 2ND BYTE TO
; BE READ
BNE
NXMAR
; NOT LAST ONE OR LAST SECOND
LAMAR
BSET
3,SMCR
; LAST SECOND, DISABLE ACK
; TRANSMITTING
BRA
NXMAR
ENMASR
BCLR
5,SMCR
; LAST ONE, GENERATE “STOP”
; SIGNAL
NXMAR
LDA
SMDR
; READ DATA AND STORE
STA
RXBUF
RTI
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