Accessing the Control/FIFO registers of NI 8422 in DOS

Question

Using the drivers niboot.exe and ni-pnp.exe driver files we are able to access the COM 1-4 ports on the card as these files create mapping of the COM ports and provides the equivalent base address however the base address of the Control Register, Transmitter/Reciever FIFO register are not specified which is necessary to monitor in order to transmitt/recieve data using the DOS and the code in C.
The solution to look for is either look for the memory/base address of the 8422 card or the function in C language which can access the Control Register, Transmitter/Reciever FIFO register of the card.
Also attacthed an document file for reference.
Thanks
bye
naru
Attachments:
NIserial .doc ‏37 KB

Answer 1

Naru,
The base address of the COM port is necessary in order to determine the I/O address of the registers on the 16550 based UART. For example, the address of the Line Control Register for COM port 1 is calculated by adding the Base Address of COM port 1 + Offset 3. The following is a table that gives the offset of each register. You can obtain more information by downloading the datasheet of the UART used by the 8422 at www.exar.com (16C654).
Register Offset
RX Buffer 0
TX Buffer 0
Interrupt Enable 2
FIFO Control Register 2
Line Control Register 3
Modem Control Register 4
Line Status Register 5
Modem Status Register 6
Scratch Register 7