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Register Descriptions Chapter 4
GPIB-1014 User Manual 4-50 © National Instruments Corporation
Function Code Registers
VMEbus Address: Base Address + 29 (hex) for Memory Function Code
Base Address + 31 (hex) for Device Function Code
Base Address + 39 (hex) for Base Function Code
Attributes: Read/Write, Internal to DMAC
7 654 321 0
X XXXXM2M1M0
R/W
On each of the four DMAC channels, there are three Function Code Registers (FCRs) associated
with the three address registers (MAR, DAR, and BAR). The three FCRs are MFCR, DFCR,
and BFCR. During a DMA cycle, when the DMAC outputs the contents of one of the three
address registers, the DMAC also outputs the associated FCR. The 3-bit value of an FCR along
with jumpers W3, W4, and W5 determine the 6-bit Address Modifier (AM) code on the
VMEbus. The AM codes are used to identify the type of cycle specified by the DMAC when the
GPIB-1014 is the bus master.
Table 3-1 shows how to program bits M2 through M0 to produce AM codes supported by the
default settings of W3, W4, and W5. Tables 3-2 shows how to program bits M2 through M0 to
produce any arbitrary AM code.
Bit Mnemonic Description
7-3r/w X Don't Care Bits
Read as zeros or ones.
2r/w M2 Supervisor/User Access Bit
If this bit is a one, the GPIB-1014 will specify Supervisor access. If it
is a zero, the GPIB-1014 will specify User access.
1r/w M1 Standard/Short Addressing Bit
If this bit is a one, the GPIB-1014 will specify a standard 24-bit cycle.
If it is a zero, the GPIB-1014 will specify a 16-bit short I/O cycle.
0r/w M0 Program/Data Access Bit
If this bit is a one, the GPIB-1014 will access program area. If it is a
zero, the GPIB-1014 will access data area.