Chapter 4
Register Descriptions
© National Instruments Corporation
4-53
GPIB-1014 User Manual
Operation Control Register
VMEbus Address:
Base A 05 (hex)
Attributes:
Read/Write, Internal to DMAC
7
6
5
4
3
2
1
0
DIR
0
SIZE
CHN
REQG
R/W
The Operation Control Register (OCR) is an operation-oriented register.
Bit
Mnemonic
Description
7r/w
DIR
Direction Bit
The Direction bit specifies the direction of the transfer, to or from
VMEbus memory :
0
=
Transfer from memory to device
1
=
Transfer from device to memory
In GPIB applications, 0 indicates transfers from memory to GPIB and
1 indicates transfers from GPIB to memory.
6r/w
0
Reserved Bit
Write zero to this bit.
5-4r/w
SIZE
Size Bits 5 through 4
The Size bits indicate the size of the data transfer. For the GPIB-1014
GPIB transfers, the size is always byte 00. For memory-to-memory
transfers, the size can be byte, word, or long-word.
00 =
Byte (8 bits)
01 =
Word (16 bits)
10 =
Long-word (32 bits)
11 =
(undefined, reserved)
3-2r/w
CHN
Chain Bits 3 through 2
The Chain bits are used to indicate what type of chaining, if any, is
used:
00 =
Chain operation is disabled
01 =
(undefined, reserved)