NI-VISA version 1.1 and later supports interaction with parallel ports as well as serial ports on your computer. The parallel ports, LPT1 through LPT4, are automatically mapped to the ASRL10 through ASRL13 resource descriptor values. (ASRL1 through ASRL9 correspond to the COM1 through COM9 serial ports on your computer.) You can use NI-VISA's included VIs to communicate with parallel ports in the same way you communicate with serial ports.
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Note You may receive unexpected errors while attempting to write to a parallel port if you leave floating pins. Unlike the serial ports, parallel ports have pins that, if left floating, cause the port driver to assume that the attached device is busy (pin 11) or out of paper (pin 12). Ground pins 11 and 12 on the port to ensure that you can write successfully to the port. |
You can also configure NI-VISA to read more serial ports, by assigning ASRL10 or higher to a serial port rather than a parallel port. NI-VISA 1.2 supports up to 32 serial ports, and NI-VISA 2.0 supports up to 128 serial ports. To reassign the ASRL resource descriptors, modify the visaconf.ini file in your VXIpnp\Winxx\NIvisa folder (where Winxx refers to your operating system).
The following example illustrates a situation where ASRL10::INSTR refers to COM10 and ASRL11::INSTR refers to LPT1.
[ASRL-RSRC-ALIAS]
Name0 = "ASRL10::INSTR"
Alias0 = ""
Enabled0 = 1
Static0 = 1
SystemName0 = "COM10"
BaudRate0 = 0
DataBits0 = 0
Parity0 = 0
StopBits0 = 0
FlowCtrl0 = 0
Name1 = "ASRL11::INSTR"
Alias1 = ""
Enabled1 = 0
Static1 = 1
SystemName1 = "LPT1"
BaudRate1 = 0
DataBits1 = 0
Parity1 = 0
StopBits1 = 0
FlowCtrl1 = 0