Rabbit OP7100 User Manual download pdf (Page 43)

OP7100 Hardware

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Z180 Serial Ports

The Z180’s two independent, full-duplex asynchronous serial channels

have a separate baud-rate generator for each channel. The baud rate can be

divided down from the microprocessor clock, or from an external clock for

either or both channels.

The serial ports have a multiprocessor communications feature. When

enabled, this feature adds an extra bit to the transmitted character (where

the parity bit would normally go). Receiving Z180s can be programmed to

ignore all received characters except those with the extra multiprocessing

bits enabled. This provides a 1-byte attention message that can be used to

wake up a processor without the processor having to intelligently monitor

all traffic on a shared communications link.

The block diagram in Figure 3-22 shows Serial Channel 0. Serial Chan-

nel 1 is similar, but control lines for /RTS and /DCD do not exist. The five

unshaded registers shown in Figure 3-22 are directly accessible as internal

registers.

Figure 3-22. Z180 Serial Channel 0

Microprocessor Internal Bus

RDR0 TDR0

TSR0RXA0 TXA0

Shift Register Ou

Shift Register In

Baud-Rate

Generator

CKA0

CNTLA0

STAT0

CNTLB0

/RTS0

/CTS0

/DCD0

RSR0

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Rabbit OP7100 User Manual Page 43