1553BBC-XX Datasheet, PDF (16/30 Pages) Actel Corporation – Core1553BBC MIL-STD-1553B Bus Controller

Core1553BBC MIL-STD-1553B Bus Controller
Message Block
An 8-word message block controls each message. The BC reads the 1553B command words from the message block
and will write the received status words back to message block. Message blocks must be positioned on an 8-word
memory boundary (Table 16).
Table 16 • Message Block
Offset Contents Written by Description
0
MSGCMD
CPU Type of 1553B Message
15:10
Inter-message GAP (IMG) after this message, 0 to 63µs.
When 000000, it uses the inter-message gap as set by the BC setup register.
Longer IMG values can be achieved by using the DELAY instruction between
messages.
The actual IMG may be llonger than when set by this register. The BC needs
to perform up to six memory accesses during the IMG period. If the backend
memory responds slowly, then the IMG may increase
9
'0': Normal Operation
'1': The CLOCK value at the mid-point of the data word sync is used as the
data for the synchronize with data mode code.
8:
Bus to use
'0': Bus A
'1': Bus B
7:6
Retries on Alternate Bus 0 to 3
5:4
Retries on Bus 0 to 3
3:0
0000
0
BC-to-RT
0001
1
RT-to-BC
0110
6
Mode Code with no data
0010
2
Mode Code RT RX with data
0011
3
Mode Code RT TX with data
0101
5
RT-to-RT
1000
8
Broadcast BC-to-RT
1110
E
Broadcast Mode Code RT with no data
1010
A
Broadcast Mode Code RX with data
1101
D
Broadcast RT-to-RT
Others Illegal
1
CW
CPU 1553B Command Word. For RT-to-RT messages, this is the RX command word
2
RTRT TX CW
CPU RT-to-RT TX 1553B Command Word
3
DATAPTR CPU or BC
Data
Pointer to memory location containing the 32-word data buffer. Must be on
Messages a 32-word boundary, i.e. bits 4:0 are 00000
Mode Code Mode code data word
Messages
4
SW
BC
Received status word. For RT-to-RT messages this is the status word from the TX RT
5
RTRT RX SW
BC
Received status word from the RX RT for RT-to-RT messages
16
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