Chapter 3
Theory of Operation
© National Instruments Corporation
3-3
AT-MIO-64F-5 User Manual
PC I/O Channel
PC I/O
Channel
Timing
Interface
Address
Latches
Data
Buffers
DMA
Control
Circuitry
Interrupt
Control
Circuitry
Address
Decoder
Register
Selects
Read-and-Write
Signals
Internal
Data Bus
AT-MIO-64F-5
DMA Request
AT-MIO-64F-5
DMA Acknowledge
and Terminal Count
AT-MIO-64F-5
Interrupt
Request
Address
I/O Channel
Control Lines
16
/
DMA Request
IRQ
Bus
Data
Bus
DMA
Acknowledge
Figure 3-2. PC I/O Channel Interface Circuitry Block Diagram
The PC I/O channel interface circuitry consists of address latches, address decoder circuitry, data
buffers, PC I/O channel interface timing signals, interrupt circuitry, and DMA arbitration
circuitry. The PC I/O channel interface circuitry generates the signals necessary to control and
monitor the operation of the AT-MIO-64F-5 multiple-function circuitry.
The PC I/O channel has 24 address lines; the AT-MIO-64F-5 uses 10 of these lines to decode the
board address. Therefore, the board address range is 000 to 3FF hex. SA5 through SA9 are used
to generate the board enable signal. SA0 through SA4 are used to select individual onboard
registers. The address-decoding circuitry generates the register select signals that identify which
AT-MIO-64F-5 register is being accessed. The AT-MIO-64F-5 is factory configured for a base
address of 220 hex. With this base address, all of the registers on the board will fall into the
address range of 220 hex to 23F hex. If this address range conflicts with any other equipment in
your PC, you must change the base address of the AT-MIO-64F-5 or of the other device. See
Chapter 2,
Configuration and Installation
, for more information.
The PC I/O channel interface timing signals are used to generate read-and-write signals and to
define the transfer cycle size. A transfer cycle can be either an 8-bit or a 16-bit data I/O
operation. The AT-MIO-64F-5 returns signals to the PC I/O channel to indicate when the board
has been accessed, when the board is ready for another transfer, and the data bit size of the
current I/O transfer. You must pay particular attention to the AT-MIO-64F-5 register sizes. An
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