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SERTEST  Diagnostic


Sometime in the 80's and 90's, I was working for an area that used lots of RS-232 serial ports on IBM PC family computers.
The various commercial diagnostics we had could test RS-232 serial ports, but if a port was found faulty, the description given of the failure was poor.
So I decided to write my own RS-232 serial port testing program, intended for technician use.

Before you use SERTEST, you need to read the information at here so that you understand terms such as 'internal loopback' and 'external loopback'.

SERTEST uses the same type of loopback plug that CheckIt software uses.  Make sure that you use that type (that wiring configuration); not just any old loopback plug will do.  Details of the required loopback plug are in step 4.1 below.

SERTEST can be downloaded from here.


Step 1 of 5  -  Important Information

•	SERTEST is a DOS program.
•	SERTEST was written by me for use on the IBM PC family of computers (IBM PC, IBM XT, etc.) I cannot guarantee correction operation on other computers.

Step 2 of 5  -  Select Port

Step 2.1	Run SERTEST.EXE   The main menu of SERTEST will appear.  It shows the serial ports that the POST found installed.
Step 2.2	Press the key corresponding to the port that you want to test.

You are now at the 'diagnostic' menu for the port that you selected.


Step 3 of 5  -  'Internal Loopback' Test

We will now do an 'internal loopback' test.  Reference diagram at here.

Step 3.1

Press the I key.  All eight sub-tests are expected to pass.  If any fail, there is something wrong - no point in proceeding to do any further tests in SERTEST.

Step 4 of 5  -  'External Loopback' Test

Prerequisite:  Step 3 ('internal loopback' test) passed.

We will now do an 'external loopback' test.  Reference diagram at here.

Step 4.1

Connect an RS-232 serial loopack plug to the port under test.  For the loopback plug, SERTEST requires the following pins to be connected. 25-pin connector: pins 2 and 3, pins 4 and 5, pins 6 and 8 and 20 and 22    (photo at here)   9-pin connector: pins 3 and 2, pins 7 and 8, pins 6 and 1 and 4 and 9    (diagram at here)

Step 4.2

Press the E key.  All eight sub-tests are expected to pass. If all fail: - There is something wrong - no point in proceeding to do any further tests in SERTEST. - Ensure that the required type of loopback connector is fitted.   - Incorrectly constructed loopback connector ? - If multiple serial ports, is the loopback connector on the right port ? If only one/some fail: - There is something wrong - no point in proceeding to do any further tests in SERTEST. - Ensure that the required type of loopback connector is fitted. - Incorrectly constructed loopback connector ? - Faulty level converter chip ?

Step 5 of 5  -  'Interrupt' Test

Prerequisite:  Both steps 3 ('internal loopback' test) and 4 ('external loopback' test) passed.
Prerequisite:  The required type of loopback connector is fitted.

We will now verify that the port can generate either hardware interrupt 4 (IRQ4) or hardware interrupt 3 (IRQ3), for various conditions.
If the port is at I/O address 3F8, then expected is interrupt 4.
If the port is at I/O address 2F8, then expected is interrupt 3.

Step 5.1

Press the I key.  All five sub-tests are expected to pass.