ST16C552 Exar Corporation, ST16C552 Datasheet - Page 15

• Manufacturer Part Number: ST16C552
• Description: DUAL UART WITH 16-BYTE FIFO AND PARALLEL PRINTER PORT
• Manufacturer: Exar Corporation

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
Note: 4 = don’t care
PORT DIRECTION
Input mode
Output mode
Output mode
Input mode
Rev. 3.40
Table 6, PD0-PD7 I/O DIRECTION MODE SELECTION
BIDEN
0
0
1
1
CONTROL REGISTER (D5)
X
X
(Note 4)
(Note 4)
0
1
15
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.
ST16C552/552A
I/O SELECT REGISTER
X
X
AA Hex
55 Hex
(Note 4)
(Note 4)