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A8251

Programmable Communications Interface

Altera Corporation 

a8251 Programmable Communications Interface Data Sheet

Command Instruction Register

The command instruction register controls transmitter/receiver

operations. Table 8 shows the format, signal name, and function of the

command instruction register data bits.

Table 8. Command Instruction Register Format

Data Bit

0

1

2

3

4

5

6

7

Signal Name

Transmitter enable (txen)

Data terminal ready (dtr)

Receiver enable (rxe)

Send break character (sbrk)

Error reset (er)

Request to send (rts)

Internal reset (ir)

Enter hunt (eh)

Function

A logic high enables the transmitter.

A logic high forces the ndtr signal to go low.

A logic high enables the receiver.

A logic high forces the txd signal to go low.

A logic high resets all error signals (pe, oe, fe).

A logic high forces the nrts signal to go low.

A logic high forces an internal state reset operation.

A logic high causes the receiver to “hunt” for sync characters.

The eh command is ignored during asynchronous operation.

Status Register

The status register allows the microprocessor, or other controlling device,

to examine the condition of the a8251. Table 9 shows the format, signal

name, and function of the status register data bits.

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Altera Corporation

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