AM8530 datasheet(86/194 Pages) AMD

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Data Communication Modes Functional Description

AMD

4–34

RTxC

PCLK

SYNC

Figure 4–20. SYNC as an Output

SYNC

DATA

CRC

Figure 4–21. MONOSYNC Message Format

SYN

SOH

STX

ETX

ETB

BCC

TEXT

HEADER

DIRECTION OF SERIAL DATA FLOW

Figure 4–22. BISYNC Message Format

4.10.1.2

SYNC Character Length

In Synchronous modes, the sync character length that is used during transmit and receive

operations is programmable via bit D0 of WR10.

If this bit is set to ‘0’ in MONOSYNC mode an 8-bit sync character will be used during

transmit and receive operations; however, if set to ‘1’ the 6-bit sync character option will

be selected, and only the least significant six bits of WR6 will be used during transmis-

sion, and the six high-order bits in WR7 will be used during receive.

In BISYNC mode, this bit selects between a 12- or 16-bit sync character length; however,

because the receiver requires that sync characters be left-justified in the registers, while

the transmitter requires them to be right-justified, only the receiver will work properly with

a 12-bit sync character. So if bit D0 of WR10 is set to ‘1’, the receiver will be configured to

recognize a 12-bit sync character, but the transmitter will remain configured for a 16-bit

sync character. The arrangement of the sync character in WR6 and WR7 is shown in Fig-

ure 4–23.

4.10.1.3

Receiver Initialization

The initialization sequence for the receiver in Synchronous modes is to write to WR4 first,

to select the mode, then WR10 to modify it if necessary, WR6 and WR7 to program the

sync characters and then WR3 and WR5 to select the various options. At this point the

other registers should be initialized as necessary. When all of this is complete the re-

ceiver is enabled by setting bit D0 of WR3 to ‘1’.

4.10.1.4

SYNC Character Removal

In Synchronous modes, a sync character that is not part of the data is transmitted before

data to establish character synchronization at the receiver. Once data transmission be-

gins all characters are sent continuously and in phase with each other. Since this syn-

chronizing information is only present at the beginning of a message it may happen that

during message transmission the combination of data characters may not provide suffi-

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