17
Data Device Corporation
www.ddc-web.com
BU-64743/64843/64863
C-03/03-300
The Enhanced BC's message sequence control engine provides
a high degree of flexibility for implementing major and minor
frame scheduling; capabilities for inserting asynchronous mes-
sages in the middle of a frame; to separate 1553 message data
from control/status data for the purpose of implementing double
buffering and performing bulk data transfers; for implementing
message retry schemes, including the capability for automatic
bus channel switchover for failed messages; and for reporting
various conditions to the host processor by means of four user-
defined interrupts and a general purpose queue.
In both the non-Enhanced and Enhanced BC modes, the Mini-
ACE Mark3 BC implements all MIL-STD-1553B message for-
mats. Message format is programmable on a message-by-mes-
sage basis by means of the BC Control Word and the T/R bit of
the Command Word for the respective message. The BC Control
Word allows 1553 message format, 1553A/B type RT, bus chan-
nel, self-test, and Status Word masking to be specified on an
individual message basis. In addition, automatic retries and/or
interrupt requests may be enabled or disabled for individual mes-
sages. The BC performs all error checking required by MIL-STD-
1553B. This includes validation of response time, sync type and
sync encoding, Manchester II encoding, parity, bit count, word
count, Status Word RT Address field, and various RT-to-RT
transfer errors. The Mini-ACE Mark3 BC response timeout value
is programmable with choices of 18, 22, 50, and 130 μs. The
longer response timeout values allow for operation over long
buses and/or the use of repeaters.
In its non-Enhanced Mode, the Mini-ACE Mark3 may be pro-
grammed to process BC frames of up to 512 messages with no
processor intervention. In the Enhanced BC mode, there is no
explicit limit to the number of messages that may be processed
in a frame. In both modes, it is possible to program for either sin-
gle frame or frame auto-repeat operation. In the auto-repeat
mode, the frame repetition rate may be controlled either inter-
nally, using a programmable BC frame timer, or from an external
trigger input.
ENHANCED BC MODE: MESSAGE SEQUENCE CONTROL
One of the major new architectural features of the Mini-ACE
Mark3 series is its advanced capability for BC message
sequence control. The Mini-ACE Mark3 supports highly
autonomous BC operation, which greatly offloads the operation
of the host processor.
The operation of the Mini-ACE Mark3’s message sequence
control engine is illustrated in FIGURE 2. The BC message
sequence control involves an instruction list pointer register;
an instruction list which contains multiple 2-word entries; a
message control/status stack, which contains multiple 8-word
or 10-word descriptors; and data blocks for individual mes-
sages.
The initial value of the instruction list pointer register is initialized
by the host processor (via Register 0D), and is incremented by
the BC message sequence processor (host readable via
Register 03). During operation, the message sequence control
processor fetches the operation referenced by the instruction list
pointer register from the instruction list.
Note that the pointer parameter referencing the first word of a
message's control/status block (the BC Control Word) must con-
tain an address value that is
modulo 8
. Also, note that if the
message is an RT-to-RT transfer, the pointer parameter must
contain an address value that is
modulo 16
.
OP CODES
The instruction list pointer register references a pair of words in
the BC instruction list: an op code word, followed by a parameter
word.The format of the op code word, which is illustrated in FIG-
URE 3, includes a 5-bit op code field and a 5-bit condition code
field.The op code identifies the instruction to be executed by the
BC message sequence controller.
Most of the operations are conditional, with execution dependent
on the contents of the condition code field. Bits 3-0 of the condi-
tion code field identifies a particular condition. Bit 4 of the condi-
tion code field identifies the logic sense ("1" or "0") of the select-
ed condition code on which the conditional execution is depen-
dent.TABLE 36 lists all the op codes, along with their respective
mnemonic, code value, parameter, and description. TABLE 37
defines all the condition codes.
FIGURE 3. BC OP CODE FORMAT
15
Odd
Parity
10
11
12
13
14
5
6
7
8
9
0
1
2
3
4
0
0
OpCode Field
1
1
0
Condition Code Field