CT2566 Datasheet, PDF (14/37 Pages) Aeroflex Circuit Technology – CT2566 MIL-STD-1553 to Microprocessor Interface Unit

2. Updates the Block Status Word by resetting the
SOM and setting EOM and any error bits.
3. Updates the Time Tag if used.
4. Increments the contents of the Stack Pointer by
four and increments the Message Counter by
one.
5. Initiates a message transfer beginning with new
Controller Start sequence if more messages are
to be transmitted.
6. Generates a BCEOM interrupt if enabled and no
further messages are to be transmitted.
Note that if an error is received and STOP ON
ERROR is set, the CT2566 completes the current
BCEOM sequence and then stops. The Stack Pointer
will point to the next message to be transmitted.
RTU Operation
The RTU mode is selected by setting bit 15 of the
Configuration Register to logic "1" and bit 14 to
logic "0".
RTU Initialization
For RTU operation, the user initializes the RAM as
shown in Table 4 and follows the steps shown in Figure
15, RTU Initialization Chart.
Look-Up Tables
The first 32 words of the Look-Up Table are initialized
with the addresses of the data blocks to be used when
received data from subaddress 0, 1, 2,…31. The next
32 table locations should be initialized with the address
of the data blocks to be used when the RTU is
instructed to transmit data from subaddress 0, 1,
2,…31. The data blocks may be any length sufficient to
contain the particular message as long as the data
block does not cross a 256 word boundary. Data blocks
may be shared by Look-Up Tables A and B, if desired
by the user (See Figure 16). The 1553 device can only
access the current Look-Up Table and the current
Descriptor Stack. The CPU selects the current area
through bit 13 of the Configuration Register.
Once in the RTU mode, the CT2566 will store the
command word in the fourth location of the current area
Descriptor Stack. The status of the message will be
recorded in the first location of the stack.
The data associated with the message will be
transferred to/from the data block indicated by the
Look-Up Table entry for that subaddress. If a system
Time Tag is provided by the user the CT2566 will
record the time of the SOM sequence in the second
word of the Stack entry.
When the CT2566 received an EOM pulse from the
1553 device, it resets the SOM bit in the Block Status
Word and sets the EOM bit and any error bits as
necessary. The Time Tag entry will be updated and an
EOM interrupt will be generated by the CPU, if enabled.
Table 4 – Typical RTU memory map (4K memory)
HEX ADDRESS
FUNCTION
0100
0101
0104
0105
0108-013F
0140-017F
01C0-01FF
0180-019F
01A0-01BF
0200-021F
0220-023F
0240-025F
0260-027F
•
•
0EE0-0EFF
0000-00FF
0F00-0FFF
Fixed Areas
Descriptor Stack Pointer A
Reserved
Descriptor Stack Pointer B
Reserved
Spare
Look-Up Table A
Look-Up Table B
User Defined Areas
Data Block 1
Data Block 2
Data Block 3
Data Block 4
Data Block 5
Data Block 6
•
•
Data Block 107
Descriptor Stack A
Descriptor Stack B
15
87654
0
00000000 1
CURRENT AREA B/A
(CONFIG. REG BIT 13)
TR (FROM COMMAND
WORD)
RTU SUBADDRESS BITS
(FROM COMMAND WORD)
RTU LOOK-UP TABLE ADDRESS
RTU SOM Sequence
Initiated when 1553 terminal puts a 1553 command
word on D00-D15 and pulses SOM low. The CT2566
saves the command received in an internal register.
Figure 17 illustrates the RTU Sequence of Operation
once a 1553 command word is received. Once the
command word is received, the CT2566 performs the
following steps:
1. Reads the Stack Pointer to get the address of the
current Descriptor Stack Entry.
2. Stores a SOM flag in the Block Status Word to
indicate a transfer operation is in progress.
3. Stores the Time Tag if used.
Aeroflex Circuit Technology
14
SCDCT2566 REV B 8/10/99 Plainview NY [phone]