National Instruments AT-DIO-32F, Руководство пользователя

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Chapter 4 Programming
© National Instruments Corporation 4-3 AT-DIO-32F User Manual
Register Sizes
Two different transfer sizes can be used for read and write operations with the PC: byte (8-bit),
and word (16-bit). Table 4-1 shows the size of each AT-DIO-32F register. For example, reading
the STAT Register requires a 16-bit (word) read operation at the selected address, whereas
writing to the RTSISHFT Register requires an 8-bit (byte) write operation at the selected address.
Addresses selected as 8-bit locations can also be accessed with a 16-bit operation; the upper byte
in this case should be thought of as eight don't care bits.
Register Description
Table 4-1 divides the AT-DIO-32F registers into four different register groups. A bit description
of each of the registers making up these groups is included later in this chapter.
The Configuration and Status Register Group controls the overall operation of the AT-DIO-32F
hardware. The configuration registers are used to program the digital I/O handshaking modes
and to enable DMA or interrupt requests. The status registers reflect the state of the digital I/O
handshaking, interrupt requests, and DMA requests. The registers in the Digital I/O Port Group
access the four 8-bit digital I/O ports. The Counter Register Group selects the counting mode
and initial count of the three counters. The RTSI Bus Register Group configures the RTSI bus
switch.
Register Description Format
The remainder of this section discusses each of the AT-DIO-32F registers in the order shown in
Table 4-1. Each register group is introduced, followed by a detailed bit description of each
register. The individual register description gives the address, type, word size, and bit map of the
register, followed by a description of each bit.
The register bit map shows a diagram of the register with the MSB (bit 15 for a 16-bit register,
bit 7 for an 8-bit register) shown on the left, and the LSB (bit 0) shown on the right. A square is
used to represent each bit. Each bit is labeled with a name inside this square. An asterisk (*)
after the bit name indicates that the bit is inverted (negative logic).
In many of the registers, one or more bits are labeled with Xs, indicating don't care bits. When a
register is read, these bits may appear set or cleared but should be ignored because they have no
significance. When a register is written to, setting or clearing these bit locations has no effect on
the AT-DIO-32F hardware.