ST78C34 Exar Corporation, ST78C34 Datasheet - Page 4

• Manufacturer Part Number: ST78C34
• Description: General Purpose Parallel Printer Port With 83 Byte Fifo
• Manufacturer: Exar Corporation

SYMBOL DESCRIPTION
ST78C34
-ERROR
SLCT
BUSY
-ACK
PE
INTSEL
D0-D7
INT
XTAL1
XTAL2
-CS
Symbol
Rev. 3.00
14-7
40
16
17
18
19
6
1
2
3
4
5
Pin
16-9
44
19
20
21
22
1
2
4
8
3
5
Signal
type
I/O
O
O
I
I
I
I
I
I
I
I
General purpose input or line printer error (active low, with internal
General purpose input or line printer selected (active high, with
General purpose input or line printer acknowledge (active low, with
Interrupt select mode. The external -ACK can be selected as an
pull-up). This is an output from the printer to indicate an error by
holding it low during error condition.
internal pull-up). This is an output from the printer to indicate that
the line printer has been selected.
General purpose input or line printer busy (active high, with internal
pull-up). An output from the printer to indicate printer is not ready
to accept data.
internal pull-up). An output from the printer to indicate that data has
been accepted successfully.
General purpose input or line printer paper empty (active high, with
internal pull-up). An output from the printer to indicate out of paper.
interrupt source by connecting this pin to the VCC or left open.
Connecting this pin to GND will set the interrupt to latched mode,
reading the status register resets the INT output.
Bi-directional data bus. Eight bit, three state data bus to transfer
information to or from the CPU. D0 is the least significant bit of
the data bus.
Interrupt output (selectable active low or high). To signal the state
of the printer port. This pin tracks the -ACK input pin, When -ACK
is low INT is low and when -ACK is high INT is high if selected as
active low interrupt.
Crystal input 1 or external clock input. A crystal can be connected
to this pin and XTAL2 pin to utilize the internal oscillator circuit. An
external clock can be used to clock oscillator circuit.
Crystal input 2 or buffered clock output. See XTAL1.
Chip select (active low). A low at this pin enables the ST78C34 /
CPU data transfer operation.
6-6
Pin Description