ST16C552AIJ68 datasheet(15/39 Pages) EXAR

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ST16C552/552A

Rev. 3.40

input and/or output functions. The signals have internal

pull-up resistors and can be wire-or’d. Normally, -

STROBE is used to strobe PD0-PD7 bus data into a

printer input buffer. -SLCTIN normally selects the printer

while AutoFDXT signals the printer to auto-linefeed.

Other signals provide similar printer functions but are

not bi-directional. The printer functions for these signals

are described in table 1, Symbol Description.

The interface provides a mode steering signal called

BIDEN. BIDEN controls the bi-directional 8-bit data bus

(PD0-PD7) direction, input or output. When BIDEN is a

logic 1 a single control bit (D5) in the control register

sets the input or output mode. Setting BIDEN to a logic

0 however sets an IBM interface compatible mode. In

this mode the bus direction (input/output) is set by eight

data bits in the IOSEL register. An AA (Hex) pattern

sets the input mode while a 55 (hex) pattern sets the

output mode. I/O direction is depicted in Table 6 below.

Printer Port

The 552/552A contains a general purpose 8-bit parallel

interface port that is designed to directly interface with

a CENTRONICS Printer. A number of the control/

interrupt signals and the 8-bit data bus have been

designed as bi-directional data buses. This allows the

interface to function with other device parallel data bus

applications. Signal -ACK is used to generate an -INTP

interface interrupt that would normally be connected to

the user CPU. -INTP can be made to follow the -ACK

signal, normal mode (see Figure 7) or it can be config-

ured for the latch mode. In the latch mode the interrupt

is not cleared until printer status register (SR) is read.

Another signal (INIT) can be made to function as an

outgoing or incoming interrupt, or combined with other

interrupts to provide a common wire-or interrupt output.

Interface signals -STROBE, -AutoFDXT, and -SLCTIN

are bi-directional and can be used as combinations of

Table 6, PD0-PD7 I/O DIRECTION MODE SELECTION

PORT DIRECTION

BIDEN

CONTROL REGISTER (D5)

I/O SELECT REGISTER

Input mode

X (Note 4)

AA Hex

Output mode

X (Note 4)

55 Hex

Output mode

X (Note 4)

Input mode

X (Note 4)

Note: 4 = don’t care

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