RTI-7
Last Command Register (Read Only)
The 16-bit read-only Last Command Register provides the host with last command and operational status information. The
RTI transmits the lower 11 bits of this register along with terminal address upon receipt of a Transmit Last Command mode
code. Read the Last Command Register by applying a logic zero to CS, CTRL, and a logic one to RD/WR and ADDR IN (0).
The 16-bit contents of the Last Command Register are read from data I/O pins DATA(15:0).
1.3 Mode Codes and Subaddresses
The UT1553B RTI provides subaddress and mode code
decoding meeting MIL-STD-1553B. In addition, the device
has automatic internal illegal command decoding for
reserved MIL-STD-1553B mode codes. Upon command
word validation and decode, status pins MCSA(4:0) and
MC/SA become valid. Status pin MC/SA will indicate
whether the data pins MCSA(4:0) are mode code or
subaddress information. Status Register bits 5 through 0
contain the same information as pins MCSA(4:0) and MC/
SA.
The system designer can use signals MCSA(4:0), MC/SA,
BRDCST, XMIT, and RCV to illegalize mode codes,
subaddresses, and other message formats via the Illegal
Command (ILL COMM) input (see figure 23 on
page 36).
The RTI will internally decode the following mode codes
as illegal:
- Dynamic Bus Control
- Selected Transmitter Shutdown
- Override Selected Transmitter Shutdown
- All Reserved Mode Codes
If the RTI receives one of the above mode codes, the RTI
responds by transmitting a status word with the Message
Error bit set to logic one.
Mode codes which involve data transfer are processed like
receive and transmit commands. The RTI will not generate
DMA request for Transmit Status Word and Transmit Last
Command mode codes since the information is stored
internal to the RTI.
The following mode codes require assistance from the host:
- Synchronize
- Initiate Self-Test
- Reset Remote Terminal
For example, the RTI will accept and respond to a Reset
Remote Terminal mode code; however it will not perform
a reset operation. The host must interpret the mode code and
take appropriate action.
The RTI does not define or interpret the following data
words associated with mode code commands:
- Transmit Vector Word
- Synchronize With Data Word
- Transmit Bit Word
The RTI will accept and respond to mode code with data;
the host must interpret or define the data word. The RTI will
store or retrieve the data required for mode code command
from block #1 of the receive or transmit page
.
Bit
Number
Initial
Condition
Description
0 through 10
[all 1s]
Least significant 11 bits of the last command word.
11
[0]
Busy Bit. System Register bit 10.
12
[0]
Self-test. System Register bit 11.
13
[1]
Terminal Flag Enabled. System Register bit 9.
14
[1]
Channel A/B. System Register bit 6.
15
[1]
Illegal Command. The RTI illegalized the last command.
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