Z80 datasheet(277/330 Pages) ZILOG

277 / 330 page

Z80 CPU Peripherals

User Manual

UM008101-0601

Serial Input/Output

257

“Synchronous Operation” on page 238 section for more details on the

interrupt modes.

After reset, or when the transmitter is not enabled, the Transmit Data output

is held marking. Break may be programmed to generate a spacing line.

With the transmitter fully initialized and enabled, continuous flags are

transmitted on the Transmit Data output.

An abort sequence may be sent by issuing the Send Abort command WR0

CMD1). The Send Abort command causes at least 8, but less than 14, 1s to

be sent before the line reverts to continuous flags. It is possible that the

Abort sequence (eight 1s) could follow up to five continuous 1 bits

(allowed by the zero insertion logic) and thus cause up to thirteen 1s to be

sent. Any data being transmitted and any data in the transmit buffer is lost

when an abort is issued.

When required, an extra 0 is automatically inserted when five contiguous

1s occur in the data stream. Automatic insertion does not apply to flags or

aborts.

Data Transfer and Status Monitoring

SDLC mode allows several combinations of interrupts and Wait/Ready

functions.

Data Transfer Using Interrupts

If the Transmit Interrupt Enable bit is set, an interrupt is generated when the

buffer becomes empty. The interrupt may be satisfied either by writing

another character to the transmitter or by resetting the Transmit Interrupt

Pending latch with a Reset Transmitter Pending command (WR0, CMD5).

If the interrupt is satisfied with this command and no more is written to the

transmitter, then no more transmitter interrupts occur. The result is a

Transmit Underrun condition. When another character is written and sent,

the transmitter can again become empty and interrupt the CPU. Following

the flags in an SDLC operation, the 8-bit address field, control field and

Z80 Datasheet(PDF) 277 Page - Zilog, Inc.