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Index Braille Printer Company
INDEX EVEREST SERVICE MANUAL
6.2
Centronics interface
Centronics Parallel Interface: This interface, originally designed and used by Centronics, Inc., was
copied by many other printer manufacturers to eventually become the default parallel standard for
printers. As with RS232-C this is merely a standard. Adherence to it is left totally to each vendor.
As with the RS232-C interface, the parallel interface has four categories of leads: ground, data,
control, and timing. However, the shape of the connector is different. The Centronics parallel
connector differs from a DB25 connector by having 36 pins in an amphenol type connector. Eight
of the leads are used to carry the bits of a character in parallel.
The parallel interface is unidirectional. This means that data can be sent in only one direction,
from the computer to the printer, hence software flow control is not appropriate. Only hardware
flow control is used in a parallel interface. Another difference from RS232-C is that there is the
capability to indicate the reason for a busy condition,
or why the printer can’t receive any more data. The printer can indicate that it is out of paper or
that it is off line by turning off/on the correct lead. The computer can also clear the printer’s
buffer, as well as reinitialize the printer’s control logic (reset). Depending on the printer, this can
be used to clear the different print modes.
6.1.5
Cable configuration Index - Apple McIntosh
INDEX - McIntosch
RXD 3 - 3 TXD
TXD 2 - 5 RXD -
GND 7 - 8 RDX+
4 SG
DSR 6 -1 HSK Out
DTR
DTR 20 - 2 HSK In
CTS
4
5
6.2.1
Centronics inteface standard
Signal name
pin(s)
Source Category Description
Data strobe
1, 19
IBM
Timing
A 1 microsec pulse to clock data
Data 1
2, 20
IBM
Data
Each one of these leads
Data 2
3, 21
IBM
Data
provides for a single bit of a data
Data 3
4, 22
IBM
Data
character.A high represents a
Data 4
5, 23
IBM
Data
1; a low represents a 0.
Data 5
6, 24
IBM
Data
Data 6
7, 25
IBM
Data
Data 7
8, 26
IBM
Data
Data 8
9, 27
IBM
Data
Acknowledge
10, 28 Ptr
Control
Indicates reception of a character
Busy
11, 29 Ptr
Control
Printer cannot recieve more data
PE
12
Ptr
Control
Printer out of paper
Select
13
Ptr
Control
Indicates that printer is selected.
0 volts
14
Ptr
Ground
Signal ground reference
OSCXT
15
Ptr
A 100/200 kHz signal
0 volts
16
N/A
Ground
Signal ground reference
Chassis ground
17
Ptr
Ground
Frame ground for electrical safety
+5 volts
18
Ptr
Positive voltage.
Input prime
31, 30 IBM
Control
Resets printer.
Fault
32,
Ptr
Control
Indicates a printer fault condition
Summary of Contents for Everest-D
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