Z80 datasheet(244/330 Pages) ZILOG

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7UGT /CPWCN

UM008101-0601

Serial Input/Output

224

entered in the 3-bit buffer if the data has a character length of seven or eight

bits, or is entered in the 8-bit receive shift register if the data has a length of

five or six bits.

In the Synchronous mode, the data path is determined by the phase of the

receive process currently in operation. A Synchronous Receive operation

begins with the receiver in the Hunt phase, during which the receiver

searches the incoming data stream for a bit pattern that matches the prepro-

grammed sync characters for flags in the SDLC mode. If the device is

programmed for Monosync Hunt, a match is made with a single sync char-

acter stored in WR7. In Bisync Hunt, a match is made with dual sync char-

acters stored in WR6 and WR7.

In either case, the incoming data passes through the receive sync register,

and is compared against the programmed sync character in WR6 or WR7.

In the Monosync mode, a match between the sync character programmed to

WR7 and the character assembled in the receive sync register establishes

synchronization.

In the Bisync mode, however, incoming data is shifted to the receive shift

receive sync register. The match between the assembled character in the

receive sync registers with the programmed sync character in WR6 and

WR7 establishes synchronization. When synchronization is established,

incoming data bypasses the receive sync register and directly enters the

3-bit buffer.

In the SDLC mode, incoming data first passes through the receive sync

performs zero deletion when indicated. Upon receiving five contiguous

1s, the sixth bit is inspected. If the sixth bit is a 0, it is deleted from the

data stream. If the sixth bit is a 1, the seventh bit is inspected. If the

seventh bit is a 0, a Flag sequence has been received; if it is a 1, an Abort

sequence has been received.

The reformatted data enters the 3-bit buffer and is transferred to the receive

shift register. The SDLC receive operation also begins in the Hunt phase,

Z80 Datasheet(PDF) 244 Page - Zilog, Inc.