Register Descriptions Chapter 4
GPIB-1014 User Manual 4-38 © National Instruments Corporation
Bit Mnemonic Description
1-0w HLDE Holdoff on End Bit
HLDA Holdoff on All Bit
HLDE and HLDA together determine the GPIB data receiving mode.
The four possible modes are as follows:
HLDE HLDA Data Receiving Mode
0 0 Normal Handshake
0 1 RFD Holdoff on All Data
1 0 RFD Holdoff on END
1 1 Continuous
In Normal Handshake mode, the local message rdy is generated when
data is received from the GPIB. When the received data is read from
the DIR, rdy is generated in Acceptor Not Ready State (ANRS), the
RFD message is transmitted, and the GPIB Handshake continues.
In RFD Holdoff on All Data (HLDA) mode, RFD is not sent true after
data is received until the Finish Handshake (FH) auxiliary command is
issued. Unlike Normal Handshake mode, the RFD HLDA mode does
not generate the rdy message even if the received data is read through
the DIR; that is, the GPIB RFD message is not generated.
In RFD Holdoff on End mode, operation is the same as the RFD
HLDA mode, but only when the end of the data block (EOS or END
message) is detected; that is, the END message is received or, if REOS
is set, the EOS character is received. Handshake Holdoff is released
by the FH auxiliary command.
In continuous mode, the rdy message is generated when in ANRS until
the end of the data block is detected. A Holdoff is generated at the end
of a data block. The FH auxiliary command must be issued to release
the Holdoff. The continuous mode is useful for monitoring the data
block transfer without actually participating in the transfer (no data
reception). In continuous mode, the DI bit (ISR1[0]r) is not set by the
reception of a data byte.