Core1553BBC MIL-STD-1553B Bus Controller
Bus Controller Operation
After power-up, the bus controller waits while the CPU
sets up the bus controller memory and registers. The
memory contains an instruction list, message blocks, and
data blocks. Once the instruction list, message blocks,
and data blocks are setup, the CPU starts the bus
controller. The bus controller works its way through all
the message blocks until it reaches the end of the
instruction list (Figure 6).
The instruction list contains a list of pointers to message
blocks. The message block contains the command words
transmitted on the 1553B bus and status words received
from the 1553B bus. It also contains a pointer to a data
block. The data block contains the data transmitted on
the 1553B bus, or the data received from the 1553B bus.
Instruction
List
Message
Block
Data
INSTRUCTION
PARAMETER
INSTRUCTION
PARAMETER
INSTRUCTION
PARAMETER
Block
MSGCMD
CW (RTRT RX)
CW (RTRT TX)
DATAPTR
32
Data Words
SW (RTRT TX)
SW (RTRT RX)
TSW
Figure 6 • BC Memory Usage
Table 13 • Instruction Word
Instruction List
15:13
12:8
7:4
3:0
The instruction list contains pairs of words: an instruction
and a parameter. Core1553BBC supports a broad set of
instructions allowing branching and sub-routine calls
with condition code support. This allows complex
instruction lists to be supported. The instruction contains
a 4-bit OPCODE and a 5-bit condition code field (Table 13
and Table 14).
Reserved
CONDCODE
Reserved
OPCODE
All of the OPCODES support the condition code field. If
the condition is TRUE, then the OPCODE is carried out;
otherwise, the BC continues to the next instruction. For
RT-to-RT messages, the condition code will be true if the
bit is set in either status word or not set in either status
word (Table 15 on page 14).
Table 14 • Supported Instructions
OPCODE Function Condition Code Parameter
Description
0000
0001
0010
0011
NOP
DOMSG
JUMP
N/A
Yes
Yes
Yes
N/A
No operation, jumps to next message
Process the message block
Message Block Address
New Instruction Address Jumps to the new message list address
INTR
User interrupt value
(Lower eight bits)
Force a BC interrupt
0100
0101
HALT
Yes
Yes
User interrupt value
(Lower eight bits)
Stop the BC
DELAY
Timer value
(Lower eight bits)
Loads the timer with the parameter and waits until the timer
reaches zero
v4.0
13
ACTEL [ Actel Corporation ]
