V5C Technical Manual
6-6
The V5C uses a 64x16 bit serially-accessed Electrically Erasable Programmable
Read Only Memory, or EPROM. This part is the National Semiconductor
NM93C46, and is used for storing board setup and configuration data for
SETV5C and the VME BIOS. Programming the EEPROM is facilitated through
the Serial EPROM Register (see Serial EPROM Register above). However, user
programs should make use of the EEPROM only under special circumstances.
SBS Embedded Computers can provide more information about programming the
EEPROM, including the dangers of doing so.
The EEPROM is 64 words in size. The first 43 words are used for VME setup
values and board setup information. The remaining 21 words are available for
general use.
Note: Like most EEPROM devices, the NM93C46 has a limited lifetime for
write cycles. For the NM93C46, the average device life is 10
6
write cycles.
Conservative use of the EEPROM will ensure that it lasts the life of the board.
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.
4-7
Reserved.
Serial EEPROM
Byte Swapping
Control Register
7 6 5 4 3 2 1 0
RSV
RSV
RSV
RSV
BYM1 BYM0 BYS1
BYS0
Figure 6-5
Byte Swapping Control Register (I/O 2A4H)
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