HI-6120 HOLTIC [Holt Integrated Circuits], HI-6120 Datasheet - Page 113

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

This command can be used to read a single location,
or may be used to start a multi-word read in which the
memory address pointer automatically decrements after
each word read. This is the only SPI op code that dec-
rements the memory pointer for multi-word operations.
Repeated memory pointer decrements will wrap around
the 0x0040 to 0x005F log buffer boundary.
15.2.7. Descriptor Table Prefetch Exceptions
For the SPI-interface HI-6121, the Memory Address
Pointer (register 0x000F) contains the address for each
new word read by the host. When starting a read access,
the host usually writes the memory address pointer with
the address for the first word to read. The host then uses
an SPI op code to initiate the read process. After the
Notice: There is no MAP auto-increment or data prefetch when MAP equals 0x0203, so the final two read cycles
repeat the previous read value and address.
FROM
HOST
=====
0xBC
0x0200
0x40
----
----
----
----
----
----
Command Read Operation
0x58
FROM
HI-6121
=======
<data>
<data>
<data>
<data>
<data>
<data>
----
----
----
write memory address pointer 0x000F
with current value in Interrupt Log Ad-
dress register minus 1. If the Log Ad-
dress register contains 0x0040 then
0x005F is written to memory pointer
register. Then read the addressed RAM
location, containing the last-written In-
terrupt Address Word. Then decrement
the memory address pointer, addressing
the corresponding Interrupt Information
Word.
COMMENT
==========================================
SPI op code writes memory address pointer (MAP).
The table start address written to MAP.
SPI op code to “read location addressed by MAP”
data from 0x0200 (SCK continues afterward)
data from 0x0201 (SCK continues afterward)
data from 0x0202 (SCK continues afterward)
data from 0x0203 (SCK continues afterward, Control Word next)
data from 0x0203 (SCK continues afterward, Control Word next)
data from 0x0203 (SCK stops and /CS is then negated)
HOLT INTEGRATED CIRCUITS
HI-6120, HI-6121
113
addressed word is transferred by SPI to the host, the HI-
6121 continues to read and transmit words from sequen-
tial RAM memory addresses, as long as the host con-
tinuously asserts chip select while providing SCK serial
clock pulses. After fetching each new word, the device
increments the Memory Address Pointer and prefetch-
es the data contained in the newly addressed location.
The next word is prefetched even when the host does
not ultimately read the following address. For HI-6121,
sequential reads from Descriptor Table that rely on
MAP auto-increment will stop advancing when the
next address contains a table Control Word. Properly
designed SPI transfers overcome this behavior.
Using SPI command op codes, the HI-6121 host must
consider prefetch and pointer behavior when reading
data from the Descriptor Table. Applied outside the De-
scriptor Table, the following SPI sequence would read
data from six successive memory addresses. But below,
applied within the table, the sequence gets stuck at the
fourth word read.
Here we assume the Descriptor Table starts at default
base address, 0x0200. The host first uses SPI op code
0xBC to store the table start address 0x0200 in the
Memory Address Pointer, then uses op code 0x40 (and
MAP auto-increment) to read the MAP-addressed loca-
tion and successive locations.