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IEEE 1284
General
The IEEE 1284 standard was approved in march 1994 as the Standard Signaling
Method for a Bidirectional Parallel Peripheral Interface for Personal Computers.
And is the first approved standard for parallel transmission on PCs. The idea
was to create a standard that was backward compatible with the old Centronics
standard. With the new standard higher speeds and greater distances are possible
plus there is the capability also sending to the host (bidirectional).
The maximum speed that is allow over the new parallel bus is 2 MBps (16 Mbps).
The cable length is determend by the mode that is used. Within the IEEE 1284
there are 5 different modes defined:
Compatibility mode
Nibble mode
Byte mode
Enhanced Parallel Port (EPP)
Extended Capability Port (ECP)
Compatibility mode
This one is compatible with all previous version of the parallel port. Data
rates are possible up to 150 bytes per second @ 6 meter (20 ft) with an AB-cable
or up to 150 kbps @ 10 meter (32.8 ft) with a CC-cable.
Nibble mode
This is a uni-directional interface. Only data transfers from periperal to host
are possible. Data is send from the e.g. printer to the PC in a nibbles (4
bits). Combined with the Compatibility mode this is what Hewlett Packard calls
"Bi-tronics".
For the Nibble-mode speeds of up to 50 kbps @ 6 meter (20 t) are possible. With
a CC-cable this can be increased to up to 150 kbps @ 10 meter (32.6 ft).
Byte mode
Byte mode makes it possible to send data from the peripheral to the host in
bytes (8 bits). Combined with the Compatibility mode you have a "Bidirectional
port".
Speeds are possible up to 500 kbps @ 10 meter (32.8 ft) when CC-cables are used.
EPP mode
This is a mode in which data can be transfered from host to peripheral or vice
versa, but not at the same time, so this is a half-duplex connection (mostly
used by CD-ROMs, tape-drives, harddisks).
Speeds can range from 500 kbps to up to 2 Mbps @ 6 meter (20 ft) or 10 meter
(32.8 ft) when CC-cables are used.
ECP mode
This is a mode in which data can be transfered from host to peripheral or vice
versa, but not at the same time, so this is a half-duplex connection (mostly
used by printers and scanners).
Speeds can range from 500 kbps to up to 1 Mbps @ 6 meter (20 ft) or 10 meter
(32.8 ft) when CC-cables are used.
Every device can only be in one mode at a time. So the IEEE 1284 workgroup
invented a way of determining which mode should be used with which device, that
is called Negotiation. The Negotiation part doesn't affect older devices, but
IEEE 1284 compliant devices can tell the host what they are and which mode to
use.
Cables and Connectors
The IEEE defined three types of connectors and six types of cables. The type A
connector is the parallel port connector (Sub-D25) found on most computers. The
type B connector is what is usually called the Centronics connector. And there
is a new connector that is called MDR36 and which is called type C. The pinning
for the Centronics and Sub-D25 is not changed.
The different cables that are defined are:
AMAM Type A male to type A male
AMAF Type A male to type A female
AB Type A male to type B
AC Type A male to type C
BC Type B male to type C
CC Type C male to type C
Also the cable characteristics are defined:
The cable shield must be connected to the connector back shell using a 360°
concentric method
The shield must be minimal 85 % optical braid coverage over foil
The maximum crosstalk is not greater then 10 %
All signals are send over a twisted pair with their signal ground return
Each pair must have an impedance of 62 ± 6 ohms @ 4 to 16 MHz
Pinning Sub-D25 A-connector
Male Female
Pin Signal Abbr. Source
1 Data Strobe (low) STROBE Computer
2 Data Bit 1 (LSB) D1 Computer
3 Data Bit 2 D2 Computer
4 Data Bit 3 D3 Computer
5 Data Bit 4 D4 Computer
6 Data Bit 5 D5 Computer
7 Data Bit 6 D6 Computer
8 Data Bit 7 D7 Computer
9 Data Bit 8 (LSB) D8 Computer
10 Acknowledge (low) ACK Printer
11 Busy (high) BUSY Printer
12 Paper End (high) PE Printer
13 Select (high) SEL Printer
14 Auto Line Feed (low) LF Computer
15 Error (low) ERROR Printer
16 Initialize Printer (prime-low) PRIME Computer
17 Select Input (low) SEL Computer
18 Return/ground GND -
19 Return/ground GND -
20 Return/ground GND -
21 Return/ground GND -
22 Return/ground GND -
23 Return/ground GND -
24 Return/ground GND -
25 Return/ground GND -
Pinning 36 pin Amphenol B-connector
Male Female
Pin Signal Abbr. Source
1 Data Strobe (low) STROBE Computer
2 Data Bit 1 (LSB) D1 Computer
3 Data Bit 2 D2 Computer
4 Data Bit 3 D3 Computer
5 Data Bit 4 D4 Computer
6 Data Bit 5 D5 Computer
7 Data Bit 6 D6 Computer
8 Data Bit 7 D7 Computer
9 Data Bit 8 (LSB) D8 Computer
10 Acknowledge (low) ACK Printer
11 Busy (high) BUSY Printer
12 Paper End (high) PE Printer
13 Select (high) SEL Printer
14 Supply Ground -
15 Oscillator Transmit Printer
16 Logical Ground -
17 Chassis Ground -
18 +5 Vdc +V Printer
19 Return Data Strobe -
20 Return Data Bit 1 -
21 Return Data Bit 2 -
22 Return Data Bit 3 -
23 Return Data Bit 4 -
24 Return Data Bit 5 -
25 Return Data Bit 6 -
26 Return Data Bit 7 -
27 Return Data Bit 8 -
28 Return ACK -
29 Return BUSY -
30 Return Input Prime -
31 Input Prime (low) Computer
32 Fault (low) FAULT Printer
33 - - -
34 - - -
35 - - -
36 - - -
Pinning MDR 36 pins C-connector
Male Female
Pin Signal Abbr. Source
1 Busy (high) BUSY Printer
2 Select (active high) SEL Printer
3 Acknowledge (active low) ACK Printer
4 Error (Fault- active low) ERROR Printer
5 Paper Error (active high PE Printer
6 Data Bit 0 (LSB) D0 Computer
7 Data Bit 1 D1 Computer/Printer
8 Data Bit 2 D2 Computer/Printer
9 Data Bit 3 D3 Computer/Printer
10 Data Bit 4 D4 Computer/Printer
11 Data Bit 5 D5 Computer/Printer
12 Data Bit 6 D6 Computer/Printer
13 Data Bit 7 (MSB) D7 Computer/Printer
14 Initial INIT
15 Data Strobe (low) STROBE Computer
16 Select Input (active low) SI
17 Auto Line Feed (active low) ALF
18 Host Logic High HLH Computer
19 Return/Ground RGND
20 Return/Ground RGND
21 Return/Ground RGND
22 Return/Ground RGND
23 Return/Ground RGND
24 Return/Ground RGND
25 Return/Ground RGND
26 Return/Ground RGND
27 Return/Ground RGND
28 Return/Ground RGND
29 Return/Ground RGND
30 Return/Ground RGND
31 Return/Ground RGND
32 Return/Ground RGND
33 Return/Ground RGND
34 Return/Ground RGND
35 Return/Ground RGND
36 Peripheral Logic High PLH Printer
Functional Description
STROBE Active low pulse used to transfer data into the printer. Pulse with must
be between 0.5 and 500 microseconds for most printers.
ACK Active low pulse indicates that data has been received and the printer is
ready to accept more.
BUSY A high signal indicates that the printer cannot receive data.
PE A high signal indicates that the printer is out of paper (Paper End)
SELECT OUT A high signal indicates that the printer is on-line
AUTO FEED A low signal indicates to the printer that a line feed is required
after each Carriage return. This signal is used as a ground line by some
manufacturers.
OSCXT A 100-200 KHz signal used by true Centronics printers only.
+5V +5Vdc Not provided by all manufacturers
PRIME A low signal resets the printer to its power-up state and the printer
buffer is cleared
FAULT A low signal indicates that the printer is in an off-line or error state
LINE COUNT Used by true Centronics printers only. Most of the time not used
LINE COUNT See 34
SELECT IN A high signal indicates to the printer that a DC1/ DC3 code is valid.
This signal is used by a few manufacturers
Host Logic High A high signal indicates that the host is alive (turned on).
Specific IEEE 1284 signal.
Peripheral Logic High A high signal indicates that the peripheral (printer) is
alive (turned on). Specific IEEE 1284 signal.
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