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Once initialized, it is not necessary for a command instruction to
precede all data transactions, only those transmissions that require a
change in the command instruction.
Am9551 MODE INSTRUCTION WORD FORMAT
The mode instruct i on word defi nes the general characteri st i c of the
Am9551.
Once the mode instruction has been written, syhc characters or
command instructions can be inserted.
The mode instruction word
defines the following:
•
For synchronous mode:
Character length
Parity enable/disable
Even/odd parity
Character synchronization
Single or double character
Sync
•
For asynchronous mode:
Baud rate multiplier
Character
' I
ength
Parity enable/disable
Even/odd pari ty
Number of stop bits
The mode instruct i on word formats for synchronous and asynchronous
modes are shown in figures 3-3 and 3-4 respectively.
Am9551 SYNC CHARACTERS
In the synchronous mode, one or two sync characters must be written to
the command regi stet".
The format of the sync characters is at the
option of the programmer.
COMMAND INSTRUCTION WORD FORMAT
The command instruction word must follow the mode and/or sync words.
Once the command word is wri tten, data can be transmi tted or recei ved
by the Am9551.
The format of the command word is shown in figure 3-5.
3-5
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