ST16C452PS Exar Corporation, ST16C452PS Datasheet - Page 12

• Manufacturer Part Number: ST16C452PS
• Description: St16c452ps -dual Uart With Parallel Printer Port
• Manufacturer: Exar Corporation

ST16C452/452PS
Printer Port
The 452/452PS 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 nor-
mally be connected to the user CPU. -INTP can be
made to follow the -ACK signal, normal mode (see
Figure 7) or it can be configured 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-direc-
tional and can be used as combinations of input and/
or output functions. The signals have internal pull-up
resistors and can be wire-or’d. Normally, -STROBE is
Note: 4 = don’t care
PORT DIRECTION
Input mode
Output mode
Output mode
Input mode
Rev. 3.20
Table 6, PD0-PD7 I/O DIRECTION MODE SELECTION [452PS only]
BIDEN
0
0
1
1
CONTROL REGISTER (D5)
X
X
(Note 4)
(Note 4)
0
1
12
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. This pin
controls the port direction in the ST16C452. A logic 0 on
this pin places the parallel port in the output mode and
a logic 1 places the parallel port in the input mode. In the
ST16C452PS, the port direction is determined as de-
scribed in Table 6. 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.
I/O SELECT REGISTER
X
X
AA Hex
55 Hex
(Note 4)
(Note 4)