HC705E5GRSSLASHD datasheet(89/148 Pages) NXP

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Motorola Bus (M Bus) Interface

Programming Considerations

MC68HC705E5 — Rev. 1.0

General Release Specification

Motorola Bus (M Bus) Interface

11.8.2 Generation of a Start Signal and the First Byte of Data Transfer

After completion of the initialization procedure, serial data can be

transmitted by selecting the master transmitter mode. If the device is

connected to a multimaster bus system, the state of the M-bus busy bit

(MBB) must be tested to check whether the serial bus is free. If the bus

is free (MBB = 0), the start condition and the first byte (the slave address)

can be sent.

An example of a program which generates the start signal and transmits

the first byte of data (slave address) is shown here. (The MMUX bit must

be set to allow control of PB7 and PB6 pins.)

SEI

; DISABLE INTERRUPT

CHFALG

BRSET

5,MSR,CHFLAG; CHECK THE MBB BIT OF THE

; STATUS REGISTER. IF IT IS

; SET, WAIT UNTIL IT IS CLEAR

TXSTART

BSET

4,MCR

; SET TRANSMIT MODE

BSET

5,MCR

; SET MASTER MODE

; i.e., GENERATE START CONDITION

LDA

#CALLING

; GET THE CALLING ADDRESS

STA

MDR

; TRANSMIT THE CALLING

; ADDRESS

CLI

; ENABLE INTERRUPT

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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