Data In Register (Dir) - National Instruments Corporation GPIB-1014P User Manual

Section Four

Data In Register (DIR)

VMEbus Address:
Attributes:
7 6
DI6
DI7
The Data In Register (DIR) is used to move data from the GPIB to the VMEbus when the interface
is a Listener. Incoming information is separately latched by this register and is not destroyed by a
write to the Command/Data Out Register (CDOR) which locates at the same address. The GPIB
Ready For Data (RFD) message is held false until the byte is removed from the DIR by an I/O read
from a VMEbus master. The Acceptor Handshake (AH) completes automatically after the byte has
been read. In RFD Holdoff mode (refer to Auxiliary Register A, later in this section) the GPIB
Handshake is not finished until the Finish Handshake (FH) auxiliary command is issued telling the
TLC to release the Holdoff. By using the RFD Holdoff mode, the same byte can be read several
times, or a GPIB Talker that is ready to provide more data can be held off until the program is
ready to proceed.
DI0 is the least significant bit of the data byte and corresponds to GPIB DIO1. DI7 is the most
significant bit of the data byte and corresponds to GPIB DIO8.
Bit Mnemonic
7-0r DIR[7-0]
© National Instruments Corporation
Base Address + 1 (hex)
Read Only
5 4
DI5 DI4
Description
Data In Bits 7 through 0
3 2
DI3 DI2
4-7
Register Bit Descriptions
1 0 R
DI1 DI0
GPIB-1014P User Manual