National Instruments PC-DIO-24 - Manual (Page 24)

Chapter 2 Configuration and Installation
© National Instruments Corporation 2-7 PC-DIO-24 User Manual
Signal Connection Descriptions
Pin Signal Name Description
1, 3, 5, 7, 9, 11, 13,
15 PC<7..0> Port C—Bidirectional data lines for port C. PC7 is the MSB,
PC0 the LSB.
17, 19, 21, 23, 25,
27, 29, 31 PB<7..0> Port B—Bidirectional data lines for port B. PB7 is the MSB,
PB0 the LSB.
33, 35, 37, 39, 41,
43, 45, 47 PA<7..0> Port A—Bidirectional data lines for port B. PA7 is the MSB,
PA0 the LSB.
49 (see note below) +5 V +5 Volts—This pin provides +5 VDC.
All even-numbered
pins GND Ground—These signals are connected to the PC ground signal.
Note: Pin 49 is connected to the +5 V PC power supply via a 1 A fuse. A replacement fuse is available from
Allied Electronics, part number 845-2007, or Littelfuse, part number 251001.
The absolute maximum voltage input rating is -0.5 to +5.5 V with respect to GND.
Port C Pin Assignments
The signals assigned to port C depend on the mode in which the 82C55A is programmed. In
mode 0, port C is considered two 4-bit I/O ports. In modes 1 and 2, port C is used for status and
handshaking signals with two or three I/O bits mixed in. Table 2-2 summarizes the signal
assignments of port C for each programmable mode. See Chapter 4, Register-Level
Programming, for register-level programming information.
Warning: During programming, note that each time a port is configured, output ports A
and C are reset to 0, and output port B is undefined.
Table 2-2. Port C Signal Assignments
Programming Mode Group A Group B
PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0
Mode 0 I/O I/O I/O I/O I/O I/O I/O I/O
Mode 1 Input I/O I/O IBFA STBA* INTRA STBB* IBFBB INTRB
Mode 1 Output OBFA* ACKA* I/O I/O INTRA ACKB* OBFB* INTRB
Mode 2 OBFA* ACKA* IBFA STBA* INTRA I/O I/O I/O
* Indicates that the signal is active low.