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A8251

Programmable Communications Interface

Altera Corporation 

a8251 Programmable Communications Interface Data Sheet

Table 7. Mode Instruction Register Bits (Synchronous Operation)

Data Bit

0

1

2

3

4

5

6

7

Bit Name

Baud rate factor (b1)

Baud rate factor (b2)

Word length select (l1)

Word length select (l2)

Parity select (pen)

Parity select (ep)

External sync detect (esd)

Single character sync (scs)

Baud Rate Factor

When programmed for synchronous operation, the MIR’s baud rate factor

bits (bit 0 and bit 1) are always a logic low.

Word Length Select

Bits 2 and 3 (l1, l2) of the MIR are the word length select bits, which are

used to select the word length of the data byte. These bits function

identically when programmed for asynchronous or synchronous

operation.

Parity Select

Bits 4 and 5 (pen, ep) of the MIR are the parity select bits, which are used

to select the parity options. These bits function identically when

programmed for asynchronous or synchronous operation.

External Sync Detect

When bit 6 (esd) of the MIR is high, external sync detection is used by the

a8251 receiver. Otherwise the receiver is responsible for sync detection.

Single Character Sync

When bit 7 (scs) of the MIR is high, the receiver looks for a single sync

character before beginning the synchronization process. Otherwise the

receiver looks for two sync characters.

Altera Corporation

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