参数资料
型号: BU-61743G4-192L
厂商: DATA DEVICE CORP
元件分类: 微控制器/微处理器
英文描述: 2 CHANNEL(S), 1M bps, MIL-STD-1553 CONTROLLER, MQFP72
封装: GULL WING, PACKAGE-72
文件页数: 8/56页
文件大小: 321K
代理商: BU-61743G4-192L
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.
Eight of the condition codes (8 through F) are set or cleared as
the result of the most recent message. The other eight are
defined as "General Purpose" condition codes GP0 through
GP7. There are three mechanisms for programming the values of
the General Purpose Condition Code bits: (1) They may be set,
cleared, or toggled by the host processor, by means of the BC
GENERAL PURPOSE FLAG REGISTER; (2) they may be set,
cleared, or toggled by the BC message sequence control
processor, by means of the GP Flag Bits (FLG) instruction; and
(3) GP0 and GP1 only (but none of the others) may be set or
cleared by means of the BC message sequence control proces-
sor's Compare Frame Timer (CFT) or Compare Message Timer
(CMT) instructions.
The host processor also has read-only access to the BC condi-
tion codes by means of the BC CONDITION CODE REGISTER.
Note that four (4) instructions are unconditional. These are
Compare to Frame Timer (CFT), Compare to Message Timer
(CMT), GP Flag Bits (FLG), and Execute and Flip (XQF). For
these instructions, the Condition Code Field is "don't care". That
is, these instructions are always executed, regardless of the
result of the condition code test.
All of the other instructions are conditional. That is, they will only
be executed if the condition code specified by the condition code
field in the op code word tests true. If the condition code field
tests false, the instruction list pointer will skip down to the next
instruction.
As shown in TABLE 36, many of the operations include a single-
word parameter. For an XEQ (execute message) operation, the
parameter is a pointer to the start of the message’s Control /
Status block. For other operations, the parameter may be an
address, a time value, an interrupt pattern, a mechanism to set
or clear general purpose flag bits, or an immediate value. For
several op codes, the parameter is "don't care" (not used).
As described above, some of the op codes will cause the mes-
sage sequence control processor to execute messages. In this
case, the parameter references the first word of a message
Control/Status block. With the exception of RT-to-RT transfer
messages, all message status/control blocks are eight words
long: a block control word, time-to-next-message parameter,
data block pointer, command word, status word, loopback word,
block status word, and time tag word.
In the case of an RT-to-RT transfer message, the size of the mes-
sage control/status block increases to 16 words. However, in this
case, the last six words are not used; the ninth and tenth words
are for the second command word and second status word.
The third word in the message control/status block is a pointer
that references the first word of the message's data word block.
Note that the data word block stores only data words, which are
to be either transmitted or received by the BC. By segregating
data words from command words, status words, and other con-
trol and "housekeeping" functions, this architecture enables the
use of convenient, usable data structures, such as circular
buffers and double buffers.
Other operations support program flow control; i.e., jump and call
capability. The call capability includes maintenance of a call stack
which supports a maximum of four (4) entries; there is also a
return instruction. In the case of a call stack overrun or underrun,
the BC will issue a CALL STACK POINTER REGISTER ERROR
interrupt, if enabled.
Other op codes may be used to delay for a specified time; start
a new BC frame; wait for an external trigger to start a new frame;
do comparisons based on frame time and time-to-next message;
load the time tag or frame time registers; halt; and issue host
interrupts. In the case of host interrupts, the message control
processor passes a 4-bit user-defined interrupt vector to the
host, by means of the Enhanced Mini-ACE's Interrupt Status
Register.
The purpose of the FLG instruction is to enable the message
sequence controller to set, clear, or toggle the value(s) of any or
all of the eight general purpose condition flags.
16
FIGURE 3. BC OP CODE FORMAT
15
10
11
12
13
14
5
6
7
8
9
0
1
2
3
4
1
0
OpCode Field
1
0
Condition Code Field
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