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Ever tried to test a serial or parallel port and wondered what this "Wrap Plug" is they mention in some publications or within the diagnostics? Here are some diagrams that might help to build own wrap plugs and some hints how to use them.
Introduction "What's a Wrap Plug anyway?" In brief it is a plug with some connections, where data lines of serial/parallel port are shorted to create loopback connection. "What's the use of a Wrap Plug?" It is used to test if the external communication from a port works as well, i.e. that port drivers and the connector itself is in working order. "Can you give an example?" I sure can. Here's the most common:
Assumed you have a PS/2 and have some trouble with i.e. the serial port. You start your machine with the reference disk or from the reference partition. At the reference' Main Menu you press [CTRL]+[A] to start the advanced diagnostics and select "Run system checkout" from the follow-up menu. Use "Run the tests one time". Then select the (first) serial port, sometimes named as "Async 1". After some time a window similar to this below appears:
+-------------------------------------------+ | Question Page 1 of 1 | | | | Do you want to use a wrap plug to test | | system-board async port 1? | | | | | | | | | | | | Press Y or N | +-------------------------------------------+ If you answer with "N" only the internal part of the serial port is tested (the UART and the Interrupt requests) but not the external transceivers. If they are damaged -by what reason- the diagnostic will end with no errors, but the port may however be defective and unusable. If you answer with "Y" you get the next window:
+-------------------------------------------+ | Question Page 1 of 1 | | | | Is an IBM communications cable attached | | to system-board async port 1? | | | | | | | | | | | | Press Y or N | +-------------------------------------------+ If there is none attached (in most cases) answer with "N". Now the next window shows up:
+-------------------------------------------+ | Instructions Page 1 of 1 | | | | Connect the wrap plug to | | system-board async port 1. | | | | | | | | | | | | Enter | +-------------------------------------------+ Assumed you don't have a wrap plug attached: the system will send data to the serial port and wait for the incoming data ... but there is none coming in, because the wrap plug is missing. A red error message in a window similar to that below shows up:
+-------------------------------------------+ | Error Page 1 of 1 | | | | 10:35:00 Slot = 0 | | System Board Async Port 1 | | Error code = 00111200 | | A system-board async-port 1 error | | occured. Replace the system board | | (type #E1FE) | | | | F3=Exit | +-------------------------------------------+ "Okay - I can see that. Where can I get a Wrap Plug ?" You can buy one from IBM. There is a 3-way wrap plug available, which has one 25-pin wrap plug for the parallel port, one 25-pin and one 9-pin for the serial port. It is IBM P/N 72X8546 and looks like that:
+----------------------+
++ ++
25-pin || || 25-pin
Serial --- || 72X8546 || --- Parallel
Plug || || Plug
++ ++
+-----------+ +----+
| |
9-pin ++---++
Serial Plug ----------- +---+
It is a nice little thing - with the possible disadvantage that it won't fit on every machine and sometimes i.e. video-, network- or keyboard-cables come in the way. "Are there alternatives to this IBM part ?"
There are surely alternatives. I just wanted to be fair and mention that IBM part, because it is referenced in the handbooks very often. The next section gives the details.
Wrap Plug Schematics 9-pin serial plug You need one Sub-D female 9-pin plug and some short wires (minimum of 30AWG).
25-pin serial plug
You need one Sub-D female 25-pin plug, one 3.9 Kilo-Ohms resistor and some short wires (minimum of 30AWG).
Ed. Tom: Alternative (much simpler) version from an old PS/2 FAQ (not tested!):
25-pin parallel plug You need one Sub-D male 25-pin plug and some short wires (minimum of 30AWG).
That's all. For easier handling of the plugs you can mount the appropriate plastic housings. No need to fumble around with them and ruin the fingernails on the attempt to unplug them after testing. These 3 plugs are enough to test either serial or parallel ports from IBM planars or IBM Adapter-cards with the IBM Advanced Diagnostics. "What if I want to test i.e. Non-IBM serial cards ?"
Many card manufacturers have own testing software available on their option disks to test at least the internal card functions.
One simple way to test the external communication on a Non-IBM serial card is to plug the wrap plug to the card and run a good terminal program like Telix "Can I use these wrap plugs with other testing software ?" The serial plugs might work with other testing software as well - the parallel wrap plug most likely not. The manufacturers of the software have own preferences which output-signals they use to test the input-lines. And these are in most cases others than IBM used for the Advanced Diagnostic. Consult your testing software documentation, READ.ME-files or manuals if there is a pin-out for the required wrap plugs. |