HC705E5GRSSLASHD datasheet(92/148 Pages) NXP

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Motorola Bus (M Bus) Interface

General Release Specification

MC68HC705E5 — Rev. 1.0

Motorola Bus (M Bus) Interface

11.8.5 Generation of a Repeated Start Signal

If at the end of data transfer the master still wants to communicate on the

bus, it can generate another start signal followed by another slave

address without first generating a stop signal. A program example is

shown here.

RESTART

BCLR

5,MCR

; ANOTHER START (RESTART) IS

BSET

5,MCR

; GENERATED BY THESE TWO

; CONSEQUENCE INSTRUCTION

LDA

#CALLING

; GET THE CALLING ADDRESS

STA

MDR

; TRANSMIT THE CALLING

; ADDRESS

11.8.6 Slave Mode

In the slave service routine, the master addressed as slave bit (MAAS)

should be tested to see if a calling of its own address has just been

received. If MAAS is set, software should set the transmit/receive mode

select bit (MTX bit of MCR) according to the R/W command bit (SRW).

Writing to the MCR clears the MAAS automatically. A data transfer may

then be initiated by writing information to MDR or dummy reading from

MDR.

In the slave transmitter routine, the received acknowledge bit (RXAK)

must be tested before transmitting the next byte of data. If RXAK is set,

indicating an end of the data signal from the master receiver, then RXAK

must switch from transmitter mode to receiver mode by software. A

dummy read must follow to release the SCL line so that the master can

generate a stop signal.

11.8.7 Arbitration Lost

If more than one master wants to engage the bus simultaneously, only

one master wins and the others lose arbitration. The arbitration loss

devices immediately switch to slave receive mode by hardware. Their

data output to the SDA line is stopped, but the internal transmitting clock

still runs until the end of the current byte transmission. An interrupt

occurs when this dummy byte transmission is accomplished with

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705E5GRS/D Datasheet(PDF) 92 Page - NXP Semiconductors

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