HI-6121PQMF HOLTIC [Holt Integrated Circuits], HI-6121PQMF Datasheet - Page 29

• Manufacturer Part Number: HI-6121PQMF
• Description: MIL-STD-1553 Remote Terminal ICs
• Manufacturer: HOLTIC [Holt Integrated Circuits]

COMMAND ILLEGALIZATION TABLE
The following pages describe various structures residing in
the RAM shared between the host and HI-6120 or HI-6121
command processing logic. The host initializes these
structures to control the terminal’s response to received
commands. The first structure described is the command
Illegalization Table used for “illegal command detection”.
Illegal command detection is an optional process. When
illegal command detection is not used, the terminal
“responds in form” to all valid commands: it sends Clear
Status and transacts the number of data words defined in
the received command. When illegal command detection
is not used, the bus controller cannot tell whether the
command is legal or illegal, from the terminal’s transmitted
response.
If illegal command detection is used, the terminal responds
differently when an illegal command is detected. The
terminal responds to illegal commands with “message
error” status, transmitting only status word. Data word
transmission is suppressed if the command type inherently
includes transmitted data words. The terminal responds to
each legal command with clear status and transacts the
number of data words defined in the type of command
received.
For consistency, apply illegal command detection to all
illegal and unimplemented commands, and to all reserved
or undefined mode code commands, or “respond in form”
to all of these commands (illegal command detection
disabled) by leaving the Illegalization Table in the all-
cleared default state after
The device uses a 256-word “Illegalization Table” in shared
RAM to distinguish between legal and illegal commands.
After the (MR) master reset input is negated, HI-6120
performs internal self test including a shared RAM test
which leaves all memory locations fully reset. Once self
test is complete, the HI-6120 READY output goes high to
indicate HI-6120 readiness for host initialization. At this
point, all entries in the Illegalization Table read logic 0, so
by default, illegal command detection is not applied.
To apply illegal command detection, the host (or auto-
initialization) writes the Illegalization Table to set bits for all
illegal command combinations. This typically includes any
unimplemented subaddresses and/or word counts,
undefined mode commands, reserved mode commands
and any mode commands not implemented in the terminal
design. Host initialization of the table can be replaced by
auto-initialization.
Once STEX is set in Configuration Register 1, terminal
execution begins. Each time a valid command is received,
a 1-bit entry (indexed using command word data bits) is
MR
master reset
HOLT INTEGRATED CIRCUITS
HI-6120, HI-6121
29
fetched from the Illegalization Table:
If fetched Illegalization Table bit equals logic 0
command is “legal”; the terminal responds “in form”,
transmitting clear status and transacting the number of
data words defined for the message type. Terminal status
is updated.
If fetched Illegalization Table bit equals logic 1
command is “illegal”; the terminal responds with status
word only, with Message Error bit set. No data words are
transmitted. Terminal status is updated.
When illegal command detection is not applied, all table
entries should read logic 0; the terminal responds “in form”
to all valid commands.
The illegalization scheme allows any subset of command
T/
and word count (or mode code number), for a total of 4,096
legal/illegal command combinations. Commands may be
illegalized down to the word count level. For example, 10-
word receive commands to a given subaddress may be
legal, while 9-word receive commands to the same
subaddress are illegal.
Broadcast receive commands are illegalized separately
from non-broadcast receive commands. Transmit and
receive commands for the same subaddress are
illegalized separately. For mode commands, any
combination of mode code number,
broadcast/non-broadcast status can be legal or illegal.
The Illegalization Table is located in shared RAM within the
fixed address range of 0x0100 to 0x01FF. See Figure 4.
The table is comprised of 256 16-bit words. To cover the
full range of 1 to 32 data words, each subaddress uses a
pair of illegalization registers. The lower register (even
memory address) covers word counts 0 to 15, using one bit
per word count. As in command encoding, “0” denotes 32
data words. Bit 0 corresponds to 32 data words, bit 1
corresponds to 1 data word and bit 15 corresponds to 15
data words. The upper register (odd memory address)
similarly covers word counts 16 to 31, using one bit per
word count. Bit 0 corresponds to 16 data words, while bit
15 corresponds to 31 data words.
When a command’s subaddress field equals 0 or 31
(0x1F), the command is a mode command. Table entries
for mode commands use bits to represent mode code
numbers, not word counts. The lower register (even
memory address) covers mode codes 0 to 15, using one bit
per mode code. Bit 0 corresponds to mode code 0, bit 15
corresponds to mode code 15. The upper register (odd
memory address) similarly covers mode codes 16 to 31,
using one bit per mode code. Bit 0 corresponds to mode
code 16, bit 15 corresponds to mode code 31. There is no
functional difference between SA0 mode commands and
R
bit, broadcast vs. non-broadcast status, subaddress
T/
R
bit and
, the
, the