V5C Technical Manual
7-2
I16 allows conversion of big-endian to little-endian on a 16-bit transfer. Sup-
ported address modes are A16, A24, and A32. Supported data mode is D16. As
can be seen from the diagram on two-byte transfer, bytes 0 and 1 are swapped.
The recommended method of controlling the byte swap mode is through the
BIOS Setup program. Under the VME system menu both slave and master byte
swapping can be set by the user. Another method of controlling byte swapping
is through the register located in ISA space.
Byte swapping can be user controlled by a register in ISA space. This register is
located at 2A4. Byte swap mode and bit settings are shown in the table below.
By changing the bits in this register the user can change the mode of byte
swapping. Note that the byte swapping mode will not be changed until the VME
bus is inactive. This prevents the byte swap mode from changing while a transfer
is in progress.
Byte Swapping Control Register
The Byte Swapping control register is used to configure the operation of the
hardware byte swapping circuitry. The register is located at I/O address 2A4.
Master
Slave
BYM1
BYM0
BYS1
BYS0
M32
0
1
0
1
I32
0
0
0
0
I16
1
0
1
0
Bit
Description
0-1
These bits control the byte swap mode when doing a VME Slave transfer.
2-3
These bits control the byte swap mode when doing a VME Master transfer.
4
If bits 0-3 are modified, the new mode is not in effect until the VMEbus is
inactive. Bit 4 of the byte swapping register is read-only and indicates when
the mode specified by by bits 0-3 is in effect.
3
2
1
0
3
2
1
0
Byte Swapping Mode
By Control Register
Mode I16
7 6 5 4 3 2 1 0
RES
RES
RES
STAT BYM1 BYM0 BYS1
BYS0
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