Z80 datasheet(260/330 Pages) ZILOG

260 / 330 page

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7UGT /CPWCN

UM008101-0601

Serial Input/Output

240

Synchronous Modes Of Operation

Monosync

In a Receive operation, matching a single sync character (8-bit sync

mode) with the programmed sync character stored in WR7 implies char-

acter synchronization and enables data transfer.

Bisync

Matching two contiguous sync characters (16-bit sync mode) with the

programmed sync characters stored in WR6 and WR7 implies character

synchronization. In both the Monosync and Bisync modes, SYNC is used

as an output, and is active for the part of the receive clock that detects the

sync character.

External Sync

In this mode, character synchronization is established externally. SYNC is

an input that indicates external character synchronization has been

achieved. After the sync pattern is detected, the external logic must wait

for two full Receive Clock cycles to activate the SYNC input. The SYNC

input must be held Low until character synchronization is lost. Character

assembly begins on the rising edge of RxC that precedes the falling edge

of SYNC.

In all cases after a reset, the receiver is in the Hunt phase, during which

the Z80 SIO looks for character synchronization. The hunt can begin only

when the receiver is enabled, and data transfer can begin only when char-

acter synchronization has been achieved. If character synchronization is

lost, the Hunt phase can be re-entered by writing a control word with the

Enter Hunt Phase bit set (WR3, D4). In the Transmit mode, the trans-

mitter always sends the programmed number of sync bits (8 or 16). In the

Z80 Datasheet(PDF) 260 Page - Zilog, Inc.