User manual

Appendix B Programmable Configurations

VMEbus Timer Limit

The VMEbus Bus Timeout (BTO) is a watchdog timer for transfers on

the VMEbus Data Transfer bus. After the specified amount of time has

elapsed, the BTO circuitry terminates a VMEbus cycle if no slave has

responded. The VXI-MXI-2 must provide the VMEbus BTO for proper

operation because when a MXIbus cycle is involved, the VMEbus

timeout must be disabled and the MXIbus BTO enabled. You should

disable the BTO of any other BTO module residing in the mainframe.

If this is not possible, set it to its maximum setting to give the MXIbus

cycles as much time as possible to complete.

The lowest value in the allowable range is 15 µs and the highest is

256 ms. The default value is 125 µs.

To change the VMEbus timeout limit of the VXI-MXI-2, write the

EEPROM byte at offset 206F hex from the VXI-MXI-2 base address.

The following table gives the value that should be written for the

corresponding time limit.

Time Limit Value (Hex)

Timer Disabled C0

15 µsC1

30 µsC2

60 µsC3

125 µs C4 (default)

250 µsC5

500 µsC6

1 ms C7

2 ms C8

4 ms C9

8 ms CA

16 ms CB

32 ms CC

64 ms CD

128 ms CE

256 ms CF