HI-6120 HOLTIC [Holt Integrated Circuits], HI-6120 Datasheet - Page 112

• Manufacturer Part Number: HI-6120
• Description: MIL-STD-1553 Remote Terminal ICs
• Manufacturer: HOLTIC [Holt Integrated Circuits]

Control Word, or may be used to start a multi-word read
because memory pointer auto-increment occurs after
the Control Word is read.
Six single-byte SPI commands add an offset to the cur-
rent address pointer value, then read the addressed
memory location; the read value is then written to the
address pointer register 15. The new pointer value is
used to start a read or write operation:
Primary use occurs when a Descriptor Table Control
Word was just read. For example, the last op code per-
formed was 0x50, reading the Control Word for the last
command. After reading the Control Word, the memory
pointer has automatically incremented. The host can ex-
amine flag bits contained in the just-read Control Word
to determine the applicable data buffer (e.g., Data Buffer
A, Data Buffer B or the Broadcast Data Buffer) then di-
rectly service that buffer using these op codes; the three
data buffer pointers occur in the three words following
the initially read Control Word.
These six commands can be used to read or write a
single location, or may be used to start a multi-word read
or write that uses the pointer’s auto-increment feature.
Command Read Operation
Command Write Operation
0xE8
0xF0
0xF8
0x68
0x70
0x78
Read the location addressed by the
memory address pointer. Write the val-
ue just read into the memory address
pointer. Then read.
Add 1 to the memory address pointer.
Read value at newly addressed loca-
tion and write it into the memory ad-
dress pointer. Then read.
Add 2 to the memory address pointer.
Read value at newly addressed loca-
tion and write it into the memory ad-
dress pointer. Then read.
Read the location addressed by the
memory address pointer. Write the val-
ue just read into the memory address
pointer. Then write.
Add 1 to the memory address pointer.
Read value at newly addressed loca-
tion and write it into the memory ad-
dress pointer. Then write.
Add 2 to the memory address pointer.
Read value at newly addressed loca-
tion and write it into the memory ad-
dress pointer. Then write.
HOLT INTEGRATED CIRCUITS
HI-6120, HI-6121
112
When some or all subaddress or mode commands are
not programmed to trigger host interrupts, a different
single-byte SPI command may be useful if polling the
Descriptor Table for message activity. In this situation,
the host may poll a series of Descriptor Table Control
Words looking for instances where the DBAC activity bit
is set. The DBAC (Descriptor Block Accessed) flag is set
in the Control Word each time the corresponding com-
mand is completed. The process of reading the Control
Word automatically resets the register’s DBAC bit so the
host can detect activity the next time the DBAC flag is
set by the device.
Since Descriptor Table Control Words are spaced four
words apart, this command is useful when polling a se-
ries of descriptor table Control Words:
Primary use occurs when the address pointer initially
points to the first Descriptor Table Control Word in a se-
ries of Control Words to be polled (every fourth word).
After 8 SCK clocks for the SPI command, each instance
of this command reads a single location using 16 SCK
clocks. If CS remains low after 24 clocks and SCK con-
tinues, a multi-word read begins, using the address
pointer’s auto-increment feature. The second word read
is at (Control Word address + 4), the next Control Word
in the table.
Another single-byte SPI command is useful when ser-
vicing interrupts. When enabled interrupts occur, two
words are written to the circular 32-word Interrupt Log
Buffer, and the Interrupt Log Address register 9 is updat-
ed to show the storage address where interrupt informa-
tion words will be stored for the next occurring interrupt.
Buffer starting address is 0x0040 and ending address
is 0x005F. Because two words are written to the buf-
fer for each interrupt, the Interrupt Log Address register
always contains an even value in the range of 0x0040
to 0x005E.
When servicing an interrupt that just occurred, the host
wants timely information on that interrupt. An SPI com-
mand is provided to simplify interrupt handling:
Command Read Operation
0x60
read addressed location then add 4 to
pointer