MC68HC05BD3 Datasheet, PDF(58/112 Page) Motorola, Inc

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MC68HC05BD3 Datasheet, PDF (58/112 Pages) Motorola, Inc – HCMOS microcontroller

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MIF bit in the interrupt routine ï¬rst. The MCF bit can be cleared by reading the M-Bus Data I/O

M-Bus I/O in the main program by monitoring the MIF bit if the interrupt is disabled. The following

is an example of a software response by a master in transmit mode in the interrupt routine (see

Figure 7-4).

ISR

TRANSMIT

BCLR

BRCLR

BRSET

LDA

STA

1,MSR

; CLEAR THE MIF FLAG

5,MCR,SLAVE ; CHECK THE MSTA FLAG,

; BRANCH IF SLAVE MODE

4,MCR,RECEIVE ; CHECK THE MODE FLAG,

; BRANCH IF IN RECEIVE MODE

0,MSR,END ; CHECK ACK FROM RECEIVER

; IF NO ACK, END OF

; TRANSMISSION

DATABUF

; GET THE NEXT BYTE OF DATA

MDR

; TRANSMIT THE DATA

7.4.4 Generation of the STOP Signal

A data transfer ends with a STOP signal generated by the master device. A master in transmit

mode can simply generate a STOP signal after all the data have been transmitted. The following

is an example showing how a STOP condition is generated by a master in transmit mode.

MASTX BRSET 0,MSR,END

LDA TXCNT

BEQ END

LDA

STA

DEC

BRA

END BCLR

EMASTX RTI

DATABUF

MDR

TXCNT

EMASTX

5,MCR

; IF NO ACK, BRANCH TO END

; GET VALUE FROM THE

; TRANSMITTING COUNTER

; IF NO MORE DATA, BRANCH TO

; END

; GET NEXT BYTE OF DATA

; TRANSMIT THE DATA

; DECREASE THE TXCNT

; EXIT

; GENERATE A STOP CONDITION

; 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 achieved 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 ï¬rst. The following is an example showing how a STOP signal is

generated by a master in receive mode.

MASR

DEC

BEQ

LDA

DECA

BNE

RXCNT

ENMASR

RXCNT

NXMAR

; LAST BYTE TO BE READ

; CHECK LAST 2ND BYTE TO BE READ

; NOT LAST ONE OR LAST SECOND

MOTOROLA

7-12

M-BUS SERIAL INTERFACE

TPG

MC68HC05BD3

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