Model T Serial Cable: Difference between revisions

Latest revision as of 13:20, 17 August 2024

Summary

The ideal cable to go from a PC to a Model 100, 102, 200, or 600, would be described as "9F/25M serial null-modem full-handshake".

That is an uncommon configuration to find in a single cable without needing adapters or needing to build it yourself custom.

The serial ports on

TRS-80/TANDY Model 100, 102, 200, 600

NEC PC-8201, PC-8201A, PC-8300, PC-8401 / Starlet, PC-8500

Olivetti M10

Kyotronic KC-85

have a DTE pinout, the same as a com port on a PC, but with a female connector, unlike a pc.

This is a backwards configuration from everything else today. This was not always the universal standard, but the universal standard today' and ever since the IBM PC, is that DTE ports (serial ports on host computers) are male (9-pin or 25-pin), and a DB25F (25-pin female) is one of 2 things: it is either a parallel printer port, or a DCE port on a peripheral (like a modem or printer), not a DTE port on a computer.

This means that most serial cables you will find today will need some sort of adapter to connect a "Model T" to anything else.

If you have a null-modem cable, it will probably have female connectors on both ends, and probably will be 9-pin on both ends. You would need either a gender-changer or a 9-to-25 adapter or both to use that.

If you have a cable with the right connectors on both ends (25 pin male and 9 pin femal), it is probably a straight-through "modem" cable, not a null-modem cable. You would need at minimum a male-to-female null-modem adapter to use that.

So a single cable with both the right wiring on the inside, and the right connectors on the outside, without needing a stack of adapters, is a little bit special. They do make them, but you just have to search for them specially. Sometimes you can find a cable with that combination of properties by searching for a "Serial Printer" cable.

Several known-good ideal cables are linked below.

The ideal cable is this:

DE9F-DB25M Serial/RS-232 Null-Modem cable

looking at cable end
female		male
DTE		DTE
Signal	DE9F	DB25M	Signal
RX	2	2	TX
TX	3	3	RX
DTR	4	6 8	DSR DCD(note)
SG	5	7	SG
DSR DCD	6 1	20	DTR
RTS	7	5	CTS
CTS	8	4	RTS

(note) Model 100 does not have anything connected to the DCD pin, so technically you could omit pin 8 on the 25-pin end of the cable, but the cable itself should still have it just to conform to standards and so there are no mystery surprises when connected to other things. Also perhaps some of the other Model T's besides Model 100 may actually have that pin connected. I haven't checked all models for that detail.

Ideal Cables

These cables are wired null-modem, have all the connections for hardware flow-control, and the right physical connectors on both ends, all in one factory-molded piece. You don't need any null-modem adapters or gender-changer adapters.

PCCables 00103

No RI

C2G 03019 Amazon CDW

S+PG

No RI

Amphenol CS-DSNL4259MF-005

S+PG

No RI

Includes nuts (removable) on the 9-pin plug screws, so if you have the wrong kind of usb-serial adapter you can still screw it to the cable.

StarTech SCNM925FM

No DCD

No RI

Software Flow Control Only Cables

These cables are not full-handshake, but still work fine for almost everything.

They are not ideal only because the RTS/CTS hardware flow control lines are either missing or faked or wired in some non-standard way. But that is not a major concern because almost nothing uses rts/cts on a Model T.

Software flow-control is the only thing any software ever used on these machines, because the system ROM doesn't contain any code to accesses the RTS/CTS pins. The hardware is present and functional, but can only be accessed from machine language programs. HTERM and TBACK are the only known examples of that.

These cables have the correct physical plugs, and correct TX/RX wiring, and have DSR/DTR at least faked, and so they work for all software flow-control applications, which is just about everything, including TPDD emulators.

Special note about TPDD emulators: TPDD clients all require that the DTR pin be connected to something. It can be faked (shorted to the machine's own DSR), or real (connected to the other ends DSR), or even wierder setups like connecting to RTS+CTS, but it has to be connected to something. A minimal 3-conductor cable can still do TPDD as long as it has DTR shorted to DSR in the DB25 plug. Many generic cables don't have that but these specific cables all do.

Monoprice 479

DCD<-->RTS+CTS

RI<-->RI

YourCableStore A63Q

DCD<-->RTS+CTS

RI<-->RI

CableWholesale 10D1-2103

DCD<-->RTS+CTS

No RI

Tripp-Lite P456-006

DCD<-->RTS+CTS

No RI

Epson CEPS-003BLK

DTR<-->DCD+RTS+CTS

No RI

svideo CC314-06-SP

DTR<-->DCD+RTS+CTS

No RI

CableWholesale 10D1-13306

DCD<-->RTS

DSR+CTS<-->DTR

No RI

This is a very unusual type of cable. If you don't have an HP or IBM plotter, I would not recommend getting this. But, strictly for the TX/RX and the physical connectors, as long as the software is ignoring RTS/CTS and DSR/DTR, it does work, so if you do have an HP or IBM plotter, then you could use this for both your plotter and your M100. It is included here simply for completeness and reference, not as a suggestion.

AYA NM9F25M-06

DCD<-->RTS+CTS

RI<-->RI

USB-Serial Adapters

Any one will work well enough. But some considerations are:

Models based on FTDI chips are generally better than the ones based on Prolific or other chips.

Try to get a usb-serial adapter that has nuts, not screws.

Here are a few ideal known-good examples.

USB-C

Gearmo GM-FTDI2-LED16-C (FTDI)
Startech ICUSB232C (Prolific)

USB

Sabrent SBT-FTDI (FTDI)
Tera Grande USB2-RS232WN-03 (FTDI)
Gearmo GM-FTDI2-LED (FTDI)
DTECH DT-5018 (FTDI, has both 9 and 25 pin connectors)
TRENDnet TU-S9 (Prolific)

Legend

For all the cable wiring notes above, the notes indicate how the cable differs from a canonical RS-232 DTE-to-DTE null-modem reference.

Any signal that is not mentioned, is wired according to the reference. IE, if TX or RX is not mentioned, then TX on one end of the cable is connected to RX on the other end of the cable.
Unless otherwise noted, the indicated wiring is symmetrical, the indicated connections are the same on both ends of the cable.

S+PG

The cable Shield (& connector shell) is connected to Protective Ground or "frame ground" (pin 1 on the DB25 connector, no pin on the DB9 just the connector shell)

RI<-->RI

Ring Iindicator is connected to Ring Indicator

DB25 pin 22 (RI) is connected to DE9 pin 9 (RI)

DCD<-->RTS+CTS

Request To Ssend is connected to Clear T Send on one end, and both are connected to Data Carrier Detect on the other end.

DB25 pins 4 (RTS) & 5 (CTS) are connected to each other, and to DE9 pin 1 (DCD).

DE9 pins 7 (RTS) & 8 (CTS) are connected to each other, and to DB25 pin 8 (DCD).

@@ Line 4: / Line 4: @@
 That is an uncommon configuration to find in a single cable without needing adapters or needing to build it yourself custom.
-The serial ports on Models 100-600 are wired DTE, the same as a com port on a PC, but with a female connector, unlike any pc.
+The serial ports on
+:TRS-80/TANDY Model 100, 102, 200, 600
+:NEC PC-8201, PC-8201A, PC-8300, PC-8401 / Starlet, PC-8500
+:Olivetti M10
+:Kyotronic KC-85
+have a DTE pinout, the same as a com port on a PC, but with a female connector, unlike a pc.
-This is a backwards configuration from everything else today. It has been suggested that maybe this is actually the original standard, and IBM came along later and changed it by putting male connectors on their PCs (probably to distinguish them from the printer port), but the standard today is that DTE ports are male. A female 25 pin port is either a parallel printer port or a DCE port on a modem.
+This is a backwards configuration from everything else today. This was not always the universal standard, but the universal standard ''today''' and ever since the IBM PC, is that DTE ports (serial ports on host computers) are male (9-pin or 25-pin), and a DB25F (25-pin female) is one of 2 things: it is either a parallel printer port, or a DCE port on a peripheral (like a modem or printer), not a DTE port on a computer.
-That means that usually you always need some kind of adapter between a PC and a M100/102/200/600, because none of the normal cables you will have lying around will have the right combination of wiring and connectors.
+This means that most serial cables you will find today will need some sort of adapter to connect a "Model T" to anything else.
-The easiest way to connect with parts you are most likely to already have lying around, is to use a common [https://www.cablewholesale.com/products/serial-modem-cable/at-modem-cables/product-10d1-02303.php 9F/25M Modem Cable] combined with a [https://www.monoprice.com/product?p_id=1203 9M/F Null-Modem Adapter].
+If you have a null-modem cable, it will probably have female connectors on both ends, and probably will be 9-pin on both ends. You would need either a gender-changer or a 9-to-25 adapter or both to use that.
+If you have a cable with the right connectors on both ends (25 pin male and 9 pin femal), it is probably a straight-through "modem" cable, not a null-modem cable. You would need at minimum a male-to-female null-modem adapter to use that.
+So a single cable with both the right wiring on the inside, and the right connectors on the outside, without needing a stack of adapters, is a little bit special. They do make them, but you just have to search for them specially. Sometimes you can find a cable with that combination of properties by searching for a "Serial Printer" cable.
+Several known-good ideal cables are linked below.
+The ideal cable is this:
+<br clear=all>
+<center>'''DE9F-DB25M Serial/RS-232 Null-Modem cable'''</center>
+{| class="wikitable" style="text-align: center; margin: auto;"
+|-
+<!-- !colspan="4"|looking at cable end!!rowspan="0"|[[File:RS-232-Null-Modem-Cable-DE9F-to-DB25M.jpg]] -->
+!colspan="4"|looking at cable end!!rowspan="0"|[[File:DE9F DB25M.jpg|400px]]
+|-
+!colspan="2"|female<br>[[File:Conn_dsub9f.gif]]!!colspan="2"|male<br>[[File:Conn_dsub25m.gif]]
+|-
+!colspan="2"|DTE!!colspan="2"|DTE
+|-
+!Signal!!DE9F!!DB25M!!Signal
+|-
+| RX || 2 || 2 || TX
+|-
+| TX || 3 || 3 || RX
+|-
+| DTR || 4 || 6<br>8 || DSR<br>DCD(note)
+|-
+| SG || 5 || 7 || SG
+|-
+| DSR<br>DCD || 6<br>1 || 20 || DTR
+|-
+| RTS || 7 || 5 || CTS
+|-
+| CTS || 8 || 4 || RTS
+|}
+<br clear=all>
+(note) Model 100 does not have anything connected to the DCD pin, so technically you could omit pin 8 on the 25-pin end of the cable, but the cable itself should still have it just to conform to standards and so there are no mystery surprises when connected to other things. Also perhaps some of the other Model T's besides Model 100 may actually have that pin connected. I haven't checked all models for that detail.
 ==Ideal Cables==
-These cables are wired null-modem, have all the connections for hardware flow-control, and the right connectors on both ends, all in one factory-molded piece. You don't need any null-modem adapters or gender-changer adapters.
+These cables are wired null-modem, have all the connections for hardware flow-control, and the right physical connectors on both ends, all in one factory-molded piece. You don't need any null-modem adapters or gender-changer adapters.
+* [https://www.pccables.com/products/00103.html PCCables 00103]
+:No RI
 * C2G 03019 [https://www.amazon.com/dp/B000083K2R/ Amazon] [https://www.cdw.com/shop/products/C2G-null-modem-cable-6-ft-white/1153481.aspx CDW]
-:DCD+DSR<-->DTR
+:S+PG
-:S+PG (Shield is also connected to pin 1 on the 25 pin connector, aka PG, Protective Ground)
 :No RI
-:Cable is thin. Good for portablity, but might mean the wires are thin and possibly not durable.
+*[https://cablesondemand.com/db25-male-to-db9-female-null-modem-cable-double-shielded-full-handshaking-cs-dsnl4259mf Amphenol CS-DSNL4259MF-005]
-*[https://www.cablesondemand.com/category/CSNULL/product/CS-DSNL4259MF/URvars/Items/Library/InfoManage/CS-DSNL4259MF.htm Amphenol CS-DSNL4259MF-005]
-:DCD+DSR<-->DTR
 :S+PG
 :No RI
-:Includes nuts (removable) on the 9-pin plug screws, so you can screw a usb-serial adapter together to the cable, no matter whether the usb-serial adapter has screws or nuts.
+:Includes nuts (removable) on the 9-pin plug screws, so if you have the wrong kind of usb-serial adapter you can still screw it to the cable.
 *[https://www.startech.com/Cables/Serial-Parallel-PS-2/DB9-DB25/10-ft-Cross-Wired-DB9-DB25-Serial-Null-Modem-Cable~SCNM925FM StarTech SCNM925FM]
 :No DCD
 :No RI
-==Ideal but Less-Ideal Cables==
+==Software Flow Control Only Cables==
-These cables actually work fine for everything(*). They are "less-ideal" only because the RTS/CTS hardware flow control lines are non-standard, or self-satisfied (shorted, looped-back), or missing. But they have the correct physical plugs, and correct TX/RX wiring, an so data and software flow-control works.
+These cables are not full-handshake, but still work fine for almost everything.
+They are not ''ideal'' only because the RTS/CTS hardware flow control lines are either missing or faked or wired in some non-standard way. But that is not a major concern because almost nothing uses rts/cts on a Model T.
+Software flow-control is the only thing any software ever used on these machines, because the system ROM doesn't contain any code to  accesses the RTS/CTS pins. The hardware is present and functional, but can only be accessed from machine language programs. [http://bitchin100.com/wiki/index.php?title=HTERM HTERM] and [https://bitchin100.com/wiki/index.php?title=TBACK TBACK] are the only known examples of that.
-And software flow-control is the only thing any of the old software ever used. The system rom doesn't even contain anything that accesses the RTS/CTS lines, not in BASIC nor TELCOM.
+These cables have the correct physical plugs, and correct TX/RX wiring, and have DSR/DTR at least faked, and so they work for all software flow-control applications, which is just about everything, including [[TPDD_Emulators|TPDD emulators]].
-But the hardware in Models 100-600 can actually do RTS/CTS, the pins are actually wired up to the uart. But to use them, you have to manipulate the UART registers yourself from a machine language program. The only software I know of that does this is [http://bitchin100.com/wiki/index.php?title=HTERM HTERM]. So these cables are NOT suitable for HTERM. (* The exception to "everything")
+Special note about TPDD emulators: [https://github.com/bkw777/dlplus/tree/master/clients TPDD clients] all require that the DTR pin be connected to something. It can be faked (shorted to the machine's own DSR), or real (connected to the other ends DSR), or even wierder setups like connecting to RTS+CTS, but it has to be connected to something. A minimal 3-conductor cable can still do TPDD as long as it has DTR shorted to DSR in the DB25 plug. Many generic cables don't have that but these specific cables all do.
-But these cables are wired null-modem and have the right connectors all in one factory-molded piece also. They don't need any null-modem adapters or gender-changer adapters. And so they are "ideal" for connecting a Model 100/102/200/600 to a pc, just, less-perfect than the ones above.
 *[https://www.monoprice.com/product?p_id=479 Monoprice 479]
 :DCD<-->RTS+CTS
-:Unlike all others: RI<-->RI
+:RI<-->RI
+*[http://www.yourcablestore.com/10-Foot-DB9-Female-DB25-Male-Null-Modem-Serial-Cable-RS232-_p_392.html YourCableStore A63Q]
+:DCD<-->RTS+CTS
+:RI<-->RI
 *[https://www.cablewholesale.com/products/serial-modem-cable/null-modem-cables/product-10d1-21303.php CableWholesale 10D1-2103]
 :DCD<-->RTS+CTS
 :No RI
-*[https://www.cablewholesale.com/products/serial-modem-cable/hp-plotter-cables/product-10d1-13306.php CableWholesale 10D1-13306]
-:This "HP PLotter" cable is bizarre.
-:DCD<-->RTS
-:DSR+CTS<-->DTR
-:No RI
-:This is a very unusual type of cable. If you don't have an HP plotter, I would not recommend getting this. But, strictly for the TX/RX and the physical connectors, as long as the software is ignoring RTS/CTS and DSR/DTR, it does work, so if you do have an HP (or IBM) plotter, then
-you could use this for both.
 *[https://www.tripplite.com/null-modem-serial-db9-serial-cable-db9-db25-female-male-6-ft~P456006/ Tripp-Lite P456-006]
 :DCD<-->RTS+CTS
@@ Line 56: / Line 97: @@
 :DTR<-->DCD+RTS+CTS
 :No RI
+*[https://www.svideo.com/cc314-06.html svideo CC314-06-SP]
+:DTR<-->DCD+RTS+CTS
+:No RI
+*[https://www.cablewholesale.com/products/serial-modem-cable/hp-plotter-cables/product-10d1-13306.php CableWholesale 10D1-13306]
+:DCD<-->RTS
+:DSR+CTS<-->DTR
+:No RI
+:This is a very unusual type of cable. If you don't have an HP or IBM plotter, I would not recommend getting this. But, strictly for the TX/RX and the physical connectors, as long as the software is ignoring RTS/CTS and DSR/DTR, it does work, so if you do have an HP or IBM plotter, then you could use this for both your plotter and your M100. It is included here simply for completeness and reference, not as a suggestion.
+* [https://www.amazon.com/dp/B078M4H4H8 AYA NM9F25M-06]
+:DCD<-->RTS+CTS
+:RI<-->RI
-==USB-Serial Adaters==
+==USB-Serial Adapters==
 Any one will work well enough. But some considerations are:
-Models based on FTDI chips are generally better than the ones based on Prolific chips.
+Models based on FTDI chips are generally better than the ones based on Prolific or other chips.
+Try to get a usb-serial adapter that has nuts, not screws.
+Here are a few ideal known-good examples.
+===USB-C===
+*[https://www.amazon.com/dp/B073ZJ6M2X/ Gearmo GM-FTDI2-LED16-C] (FTDI)
+*[https://www.amazon.com/gp/product/B074VN9ZG4/ Startech ICUSB232C] (Prolific)
+===USB===
+*[https://www.amazon.com/dp/B005SYQV9C/ Sabrent SBT-FTDI] (FTDI)
+*[https://www.amazon.com/dp/B0762BSKGC/ Tera Grande USB2-RS232WN-03] (FTDI)
+*[https://www.amazon.com/dp/B01DT6K8G2/ Gearmo GM-FTDI2-LED] (FTDI)
+*[https://www.amazon.com/dp/B01AT2FTOU/ DTECH DT-5018] (FTDI, has both 9 and 25 pin connectors)
+*[https://www.amazon.com/dp/B0007T27H8 TRENDnet TU-S9] (Prolific)
+==Legend==
+For all the cable wiring notes above, the notes indicate how the cable '''differs''' from a canonical RS-232 DTE-to-DTE null-modem reference.
+[[File:RS-232 full-handshake null-modem.png|thumb|RS-232 full-handshake null-modem]]
+<br>
+Any signal that is not mentioned, is wired according to the reference.  IE, if TX or RX is not mentioned, then TX on one end of the cable is connected to RX on the other end of the cable.<br>
+Unless otherwise noted, the indicated wiring is symmetrical, the indicated connections are the same on both ends of the cable.
+'''S+PG'''
+:The cable '''S'''hield (& connector shell) is connected to '''P'''rotective '''G'''round or "frame ground" (pin 1 on the DB25 connector, no pin on the DB9 just the connector shell)
-The serial cables all have screws in the plugs, so if you get a usb-serial adapter that has nuts (instead of screws) then the serial cable can be locked onto the usb-serial adapter with the screws.
+'''RI<-->RI'''
+:'''R'''ing '''I'''indicator is connected to '''R'''ing '''I'''ndicator
+:DB25 pin 22 (RI) is connected to DE9 pin 9 (RI)
-*[https://www.amazon.com/dp/B005SYQV9C/ Sabrent SBT-FTDI]
+'''DCD<-->RTS+CTS'''
-*[https://www.amazon.com/dp/B0762BSKGC/ Tera Grande 3ft w/ jack nuts]
+:'''R'''equest '''T'''o '''S'''send is connected to '''C'''lear '''T''' '''S'''end on one end, and both are connected to '''D'''ata '''C'''arrier '''D'''etect on the other end.
-*[https://www.amazon.com/dp/B0007T27H8/ TrendNet TU-S9] (Prolific-based, but better than most other Prolific-based)
+:DB25 pins 4 (RTS) & 5 (CTS) are connected to each other, and to DE9 pin 1 (DCD).
+:DE9 pins 7 (RTS) & 8 (CTS) are connected to each other, and to DB25 pin 8 (DCD).

Model T Serial Cable: Difference between revisions

Latest revision as of 13:20, 17 August 2024

Contents

Summary

Ideal Cables

Software Flow Control Only Cables

USB-Serial Adapters

USB-C

USB

Legend

Navigation menu

Model T Serial Cable: Difference between revisions

Latest revision as of 13:20, 17 August 2024

Summary

Ideal Cables

Software Flow Control Only Cables

USB-Serial Adapters

USB-C

USB

Legend

Navigation menu

Search