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DB-25 serial port with 16 pins [Model 90]

ardent-blue

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Jan 2, 2015
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461
While immersed in the hand to keyboard struggle to attach an IBM 6094-020 LPFK to a PS/2, I called on Michael Brutman to assist. He confirmed the bare minimum of lines needed, but he found a twist. Expect an update when he confirms it. Gist of the story - just because IBM published something only means that AT THAT TIME it was true... Maybe...

http://ps-2.kev009.com/ohland/6094/I...-020_LFPK.html the port info is "correct", but WRONG. Nothing horrible, but IBM figured that it didn't need all the wires.

But anyways, while re-assembling my Model 90, I decided to look at the DB25 serial port. There are only > 15 < pins, all other positions are empty.


The Model 90 was built from '89 to '94-ish. My hunch is that some older equipment in the mid 80s needed the extra lines. So, we have a DB25 serial [15 pins!] and a DE9.

What serial equipment from the mid 80s used a DB25 serial port with 15 pins?


IBM Model 90 DB25 Serial Port, 15 pins

DB25_15_Pin_ASCII.jpg

"x" pin
"o" empty



https://advancedrelay.com/downloads/pinouts-for-serial-interfaces.pdf

1 – No pin [IBM says N/C]
2 Transmitted Data TD (“TXD”)
3 Received Data RD (“RXD”)
4 Request to Send RTS
5 Clear to Send CTS
6 DCE Ready—“Data Set Ready” DCR (“DSR”)
7 Signal Ground—“Common Return”
8 Received Line Signal Detector—“Carrier Detect,” “Data Carrier Detect” RLSD
9 = +12 VDC reserved for testing
10 = –12 VDC reserved for testing
11 = Unassigned
12 Data Signal Rate Selector (DCE Source)
13 Secondary Clear to Send SCTS [IBM says N/C]
14 – No pin [IBM says N/C]
15 – No pin [IBM says N/C]
16 – No pin [IBM says N/C]
17 – No pin [IBM says N/C]
18 – No pin [IBM says N/C]
19 – No pin [IBM says N/C]
20 DTE Ready—“Data Terminal Ready” DTR
21 – No pin [IBM says N/C]
22 Ring Indicator RI
23 – No pin [IBM says N/C]
24 Transmitter Signal Element Timing (DTE Source)—“External Clock” [IBM says N/C]
25 – No pin [IBM says N/C]


Note that many applications use only a subset of this pinout: 16 pins—1 through 8, 15, 17, and 20 through 25—for synchronous communication with secondary control and testing; 12 pins—1 through 8, 15, 17, 20, and 22—for ordinary sync applications; 7 pins—2 through 4, 6 through 8, and 20—for asynchronous communication with flow control; or the 4 pins 2, 3, 7, and 20 for bare-bones async applications that use software flow control.

Do any of these devices ring a bell for an old style serial port?

PRINTERS
IBM PagePrinter 3812
IBM LaserPrinter 4019-001
IBM LaserPrinter 4019-E01
Proprinter (R) 4201-001
IBM Proprinter II 4201-002
IBM Proprinter III 4201-003
IBM Proprinter XL 4202-001
IBM Proprinter II XL 4202-002
IBM Proprinter III XL 4202-003
IBM Proprinter X24 4207-001
IBM Proprinter X24E 4207-002
IBM Proprinter XL24 4208-001
IBM Proprinter XL24E 4208-002
IBM Personal PagePrinter 4216-010/D10/031
Quietwriter (R) 5201-001
IBM Quietwriter 5201-002
IBM Quietwriter III 5202-001
Quickwriter (R) 5204-001
IBM PagePrinter 3816
IBM ExecJet Printer 4072
PS/1 (TM) Printer 2205 Model 001

PLOTTERS
IBM 6180 Color Plotter
IBM 6182 Auto Sheet Feed Plotter
IBM 6184 Color Plotter
IBM 6185 Color Plotter
IBM 6186 Color Plotter Model 1,2
IBM 7372 Color Plotter
IBM 7374 Color Plotter
IBM 7375 Color Plotter Model 1,2
 

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AFAIK, the standard serial port on the PS/2 could not do synchronous protocol. There was a SDLC adapter for that, if I'm remembering correctly. Hence the unused pins, which are mostly associated with sync. (See here under V.24). I remember the Bell 208 and 209 modems. A blazing 9,600 bps over a leased line was the cat's whiskers.
 
Most times all that is needed is pins 2, 3, 7 and either jumper 4 to 5 and 6 to 8 & 20. Or if hardware handshake is used then connect 4, 5, 6, 8 & 20 to handshake with the other device. But I guess you know that.
 
I'll look at the reference.

Had a flashback to common sums. 12 pins on upper pins, three pins on lower pins equals fifteen pins. Oops.

I do know of the low conductor port, but everyone that designed this port is retired, dead, or both. IBM coulda sold [and did!] a DB25 to DE9 cable. So why they ran a DB25, partially pinned, and a smaller DE9, I dunno.

https://arcelect.com/rs232.htm

Pin 1 is empty, Shield Ground
Pin 20 DTE Ready
Pin 22 Ring Indicator
Pin 24 Transmit Signal Element Timing (DTE Source)


https://ardent-tool.com/9590/190-176.txt

OTHER DEVICES
ROLMphone 244PC 46900C 21A1482
ROLMphone 120/DCM (Data Communication Module) 61300 84C9201
ROLMphone 240/DCM (Data Communication Module) 62300A 79X0405
ROLMphone 240E/DCM (Data Communication Module) 62380 21A1312
ROLMphone 400/DCM (Data Communication Module) 64300A 79X0408
ADCM (Asynchronous DCM) 42201 97D1108

ROLMphone 244PC is mentioned on the net as providing data transfer over the serial port...

Article Mentioned as having an RS--232 port.

MAKING RS-232-C COMMUNICATIONS PACKAGES WORK WITH A DIGITAL PBX
"Under the new regime, Centrex phones will be replaced with special units manufactured by
IBM/Rolm, called "ROLMphones." These can be voice-only, or voice/data. The data option
adds a 25-pin RS-232-C connector and accompanying electronics to the single-line or
multiple-line voice telephone. Through a single pair of wires, a data-equipped phone can
manage a voice conversation simultaneous with an asynchronous data connection up to
19.2 Kbit/s, using a proprietary protocol known as "ROLMlink." This single instrument
replaces the Centrex telephone, the LDS-125, and the user’s dialout modem."
 
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http://www.mcamafia.de/pdf/m90_ssi.pdf says that the serial interface on the main board is type 3

here is the manual that you should be looking at for the definitions of the type 3 serial interface on the model 90
http://www.mcamafia.de/pdf/ibm_hitrc08.pdf

The Model 90 SSI seems to lack a serial port pinout.

HITR has Pin 24 as N/C. They call it "EIA-232-D" page 45 physical. The actual Model 90 DB25 serial port pinout differs in the presence of Pins 9-11 and Pin 24. Having said that, unless these pins are actually tested, they might be truly N/C from the planar... It depends...
 
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