Theory of Operation
Chapter 3
AT-DIO-32F User Manual
3-2
© National Instruments Corporation
The AT-DIO-32F board is a full-size, 16-bit, PC I/O channel adapter. The PC I/O channel
consists of a 24-bit address bus, a 16-bit data bus, a DMA arbitration bus, interrupt lines, and
several control and support signals.
Address Decoder
The PC I/O channel has 24 address lines; the AT-DIO-32F uses ten of these lines to decode the
board address. Therefore, the board address range is hex 000 to 3FF. Address lines SA5 through
SA9 are used to generate the board enable signal. SA0 through SA4 are used to select the
onboard registers.
Bus Transceivers
The bus transceivers control the sending and receiving of the data lines to and from the PC I/O
channel.
PC I/O Channel Control Circuitry
This circuitry monitors and transmits the PC I/O channel control and support signals. The
control signals identify transfers as read or write, configuration or I/O, and 8-bit or 16-bit. A
support signal is returned to the PC I/O channel from the AT-DIO-32F to indicate the size of the
current data transfer.
Configuration and Status Registers
The AT-DIO-32F has seven configuration registers and a status register. Four 16-bit
configuration registers (CFG1, CFG2, CFG3, and CFG4) are used to program all of the digital
I/O modes of the
AT-DIO-32F. The other configuration registers are used to configure three onboard counters and
the RTSI bus and to clear certain interrupt status bits. The 16-bit status register (STAT) contains
DMA, interrupt, and handshaking signal status information. Refer to Chapter 4, Programming,
for additional information about these registers.
Data Latches and Drivers
The four 8-bit digital I/O ports are divided into two handshaking groups. Ports A and B are
assigned to handshaking Group 1. Ports C and D are assigned to handshaking Group 2. Each
port can be configured as read or write, and single-buffered or doubled-buffered. When the
board is first turned on, each port is configured as a single-buffered read port. Reading a single-
buffered input port returns the data currently available for that port at the I/O connector. Data is
latched in a read port on the appropriate active edge of the handshaking request line, REQ1 or
REQ2, when the port is configured as a double-buffered input port.
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