HC705E5GRSSLASHD datasheet(83/148 Pages) NXP

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Motorola Bus (M Bus) Interface

M-Bus Registers

MC68HC705E5 — Rev. 1.0

General Release Specification

Motorola Bus (M Bus) Interface

MTX — Transmit/Receiver Mode Select Bit

This bit selects the direction of master and slave transfers. When

addressed as a slave, this bit should be set by software according to

the SRW bit in the status register. In master mode, this bit should be

set according to the type of transfer required. Hence, for address

cycles this bit will always be high.

1 = Transmit

0 = Receive

TXAK — Transmit Acknowledge Enable Bit

If TXAK is cleared, an acknowledge signal will be sent out to the bus

at the ninth clock bit after receiving one byte of data. When TXAK is

set, there will be no acknowledge signal response (for example,

acknowledge bit = 1).

MMUX — M-Bus Multiplexer

This bit is used to enable PB7 and PB6 to be under the control of the

M-bus circuit. When set, both PB7 and PB6 become open-collector

outputs or inputs when enabled by the M-bus control. When cleared

PB7 and PB6 are under control of the port DDR logic. This bit can be

set or cleared independent of the MEN bit. Caution should be used if

PB7 and PB6 are used as general-purpose I/O.

1 = M-bus control

0 = POR condition, port B DDR control

Freescale Semiconductor, Inc.

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HC705E5GRS/D 데이터시트(PDF) 83 Page - NXP Semiconductors