Special Test,
LPT - Printer Port Test


This Page published Jan. 15, 2011. If you have comments or suggestions, I will be happy to hear about them. Scotty. [wsprowls (a.t.) yahoo.com]

The purpose of this page  is to describe the use of the Special Test, LPT-Printer Port Test. This test will verify operation of the computer's Parallel Printer Port and/or a printer cable connected to it. No MSA hardware is required to perform this test. A voltmeter is recommended for testing. Verification of the LPT can be accomplished without one by using a jumper wire, and using a "Status" pin to read a "Command" pin.

Set-Up for LPT Test:
1. Run the MSA Program.
  a. If the Program has not been run before, the Hardware Configuration Manager Window will open. Verify that the LPT Port Address is Hex 378. If you know your
LPT Port Address is different, insert it. However, the LPT Test will run, even if the address is wrong. Click "Save Configuration".
  b. Otherwise, the MSA Main Graph will open and sweep with the MSA in the Spectrum Analyzer mode.
2.
Halt the sweep.
3. Click menu item, Setup, and select Special Tests.
4. The Special Tests Window will open.
5. Click the "LPT Port Test" button.
6. A new window will open, "LPT Printer Port Test"
. It is divided into 3 areas. Commanding is on the left, Receiving is on the upper right, and Addressing is on the lower right.
7. The computer is now ready to respond to your actions within this window.

Procedure:
1. Commanding
    Click either a "0" box or "1" box associated with a particular pin of the 25 pin Parallel Printer Port Connector. The value next to the pin description will change, according to your selection. That pin on the connector should measure approximately 0 volts for a command of "0", and greater than +2.0 volts for a command of "1". An error here indicates that the LPT Port Address in the MSA software is not correct for your computer. Change the
LPT Port Address in this "LPT Printer Port Test" window. See the paragraphs following this Test Procedure. Assure Commanding is successful before proceding.

2. Receiving
    Click the "CAPTURE STATUS" button to read the "Status" port of the computer. If there is nothing connected to the
25 pin Parallel Printer Port of the computer, all status bits should indicate "1". If they do not, the possible explanation is that the computer does not have internal "pull-up" resistors. To test for this, measure the computer's LPT Parallel port, pins 10 through 13, and 15 with a voltmeter. They should read +2.0 volts or greater. If the computer does not have internal "pull-up" resistors, they must be on the MSA's Control Board.
    Even without
internal "pull-up" resistors, you can still test the status pins by using a "Command" pin as a signal source:
1. Connect a wire from pin 1 (Strobe) to pin 11 (WAIT).
2. Click
the "CAPTURE STATUS" button to read. The "Wait" box will display the state of "Strobe".
3. Change the state of pin 1 and then
click the "CAPTURE STATUS" button to read the state.
4. Move the wire. Pin 1 (Strobe) to pin 10 (ACK), and repeat the actions.
5. Do this for pins 12, 13, and 15, using pin 1 as the signal source.

3. Exiting the LPT Test Procedure
a. C
lose the "LPT Printer Port Test" window.
b. Close the Special Tests window.
c.
Click the "Restart" button in the Main MSA window. This will re-initialize the MSA software, and hardware if the MSA Control Board had been connected during the LPT Test.

Determine the Addresses of the Computer's LPT port.
The computer has allocated 3 addresses for the LPT Printer Port. They are:
"Port", "Status", and "Control". You can "ask" your computer what they are by following these steps:
From your computer's main window, click:
Start/Settings/Control Panel/System/Device Manager.
From there make selections similar to Ports/Printer Port(LPT1)/Properties/Resources. Look for the item Input/Output Range, which will display a range of numbers in Hex. The first number in that range is the "Port" address of the LPT port. It is usually the address of the LPT on the Motherboard. If an external Printer Port Card is installed in your computer, it will usually be a secondary range.
The "Status" port is a value of "1" greater than the "Port" address.
The "Control" port is a value of "2" greater than the "Port" address.
Changing the Addresses of the MSA Software.
 The address in the "LPT Port Address (Hex)" box is the "Port" Address that is in the Configuration Manager. It can be changed during this test. The value in the box is in Hexadecimal. But, you may insert a new address in either Hex or Decimal (base 10). That is, the normal value is Hex 378. The decimal equivalent is 888. If typing in a new value, either the "Hex" box or "Dec" box must be clicked. If a decimal value is entered, the displayed value will be converted to Hex when the "Dec" box is clicked. This will not change the Addresses in the Hardware Configuration Manager. You must do that manually via the menu, Setup/Hardware Config Manager.