National Instruments AT-MIO-16D, Руководство пользователя

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Chapter 4 Programming
© National Instruments Corporation 4-3 AT-MIO-16D User Manual
The Configuration and Status Register Group controls the overall operation of the AT-MIO-16D
hardware. The Event Strobe Group is a group of registers that, when written to, generate some
event on the AT-MIO-16D board. The registers in the Analog Output Group access the
AT-MIO-16D DACs. The Analog Input Group allows ADC output to be read. The
Counter/Timer Group consists of the three registers of the onboard Am9513A Counter/Timer
chip. The registers in the Digital I/O Group access the onboard digital input and output lines.
The registers in the RTSI Switch Group control the onboard RTSI switch. The DIO-24 Register
Group controls all operations and modes of the DIO-24 circuitry on the AT-MIO-16D board.
You may notice that the DIO-24 registers have the same offset as Command Register 1 and
Command Register 2. Access to the DIO-24 registers are distinguished by means of performing
an 8-bit bus transfer versus a 16-bit bus transfer.
Register Description Format
The remainder of this register description chapter discusses each of the AT-MIO-16D 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 its square. An asterisk (*) after
the bit name indicates that the bit is inverted (negative logic).
In many of the registers, several bits are labeled with an X, 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-MIO-16D hardware.
The bit map field for some write-only registers states not applicable, no bits used. Writing to
these registers generates a strobe in the AT-MIO-16D. These strobes are used to cause some
onboard event to occur. For example, they can be used to clear the analog input circuitry or to
start a data acquisition operation. The data is ignored when writing to these registers; therefore,
any bit pattern will suffice.
Configuration and Status Register Group
The three registers making up the Configuration and Status Register Group allow general control
and monitoring of the AT-MIO-16D hardware. Command Registers 1 and 2 contain bits that
control operation of several different pieces of the AT-MIO-16D hardware. The Status Register
can be used to read the state of different pieces of the AT-MIO-16D hardware.
Bit descriptions of the three registers making up the Configuration and Status Group are given on
the following pages.