WIENER, Plein & Baus GmbH
23
www.wiener-d.com
Every command sequence begins with a Command Header Word with the structure as shown
in the table below:
Bits
24 - 31
12 - 23
11
9, 10
8
6, 7
0 - 5
Function BLT=64
*
MB
*
NWR
DS=00
AM
Where
AM – VME address modifier
0x9 – for simple A32 transfers
0xB – for BLT (block transfer) and multi-BLT A32 transfers
0x39 – for A24 commands, with only simple, non-BLT transfers allowed
0x29 – for A16 commands, with only simple, non-BLT transfers allowed
NWR – 0 for write commands, 1 for read commands
DS – data strobes – both DS0 and DS1 on
MB – 0 for simple and single-BLT transfers, 1 for multi-BLT transfers
BLT – number of 32-bit transfers in a BLT; 64 (0x40) represents 256 bytes.
When multi-BLT transfer is declared, the Command Header Word is to be followed by a
NumBlocks word representing number of blocks in the multi-BLT transfer.
Next word in the command sequence is the Address Word representing here the VME
address offset only. The base address bits (the 5 most significant bits in the full VME
address) are disregarded as it is presumed to apply to the VM-DBA itself.
What is to follow the Address Word depends on the kind of transfer declared in the Header
Word, such that
(i) The Address Word is the last word in all READ command sequences – simple,
single-BLT, and multi-BLT.
(ii) In a WRITE command sequences, the Address Word is to be followed by the
number of Data Words declared in the Command Header Word. This number is 1
for simple WRITE, 64 for single-BLT WRITE, and 64*NumBlocks for multi-BLT
WRITE sequence. Note that the latter number may be quite high, equal 64*1950 in
multi-BLT WRITE to the utility FIFO.
The following limitations apply to stack preparation:
(i)
The command stack may contain many simple WRITE command sequences, but
otherwise they are to contain one and only one command sequence.
(ii)
BLT and multi BLT WRITE is valid only for the A32 offset of 0x80000 (the
utility FIFO)
