HI-6137_16 Datasheet, PDF (147/230 Pages) Holt Integrated Circuits – Compact Multi-Terminal Device with SPI Host Interface

HI-6137
15.3.3. Broadcast Message Handling in Ping-Pong Mode
For MIL-STD-1553B Notice II compliance, a remote terminal should be capable of storing data from broadcast mes-
sages separately from non-broadcast message data. Some applications may not include this requirement. The stan-
dard does not stipulate where data separation should occur (e.g., within the RT or within the external host) so the
device provides alternative strategies.
When the NOTICE2 bit in the “Remote Terminal Configuration Register (0x0017)” is 1 and the BCSTINV bit is 0,
ping-pong mode subaddresses (or mode codes) will buffer data words from broadcast and non-broadcast messages
separately. Broadcast message information and data are stored in the broadcast data buffer; non-broadcast message
information and data are stored in ping-pong buffers A and B. Since there is just one broadcast data buffer, the
NOTICE2 option treats broadcast messages as exceptions to normal ping-pong mode. When using the NOTICE2
option, broadcast data buffer servicing should have high priority, because a closely following broadcast message will
overwrite the broadcast buffer.
Every mode command and subaddress (including transmit subaddresses) must have an assigned valid
broadcast data pointer when NOTICE2 is asserted. When the NOTICE2 bit in the “Remote Terminal Configuration
Register (0x0017)” is 1 and the BCSTINV bit is 0, reception of a broadcast-transmit message updates the Message
Information and Time-Tag Words for the assigned broadcast buffer, but no data is transmitted on the bus. Since
broadcast-transmit is not allowed, multiple transmit subaddresses may share a common “bit bucket” broadcast buffer.
A two word buffer is sufficient for storing the MIW and Time-Tag Word.
When using ping-pong mode, there are two ways to handle broadcast messages, when broadcast is enabled:
Option 1 for Ping-Pong Mode Broadcast Messages:
This option isolates broadcast message information in the broadcast data buffer. If the descriptor Control Word IBR bit
and “Remote Terminal (RT) Interrupt Enable Register (0x0012)” IBR bit are both set, reception of broadcast messages
generates an INT host interrupt. To prevent data loss, the broadcast data buffer must be serviced before the next
broadcast message occurs. Broadcast messages do not affect non-broadcast message ping-pong; the Control Word
DPB bit does not toggle after broadcast message completion.
Option 1 Setup: At initialization, host asserts the NOTICE2 bit in the “Remote Terminal Configuration Register
(0x0017)” and sets the IBR (Interrupt Broadcast Received) bit in descriptor Control Word(s). The IBR bit is asserted in
the “Remote Terminal (RT) Interrupt Enable Register (0x0012)”.
When a broadcast command is received, message information and data is stored in the broadcast data buffer and
an INT interrupt is generated. The host must read the Interrupt Log to determine the originating subaddress (or mode
code), then service the broadcast data buffer for that subaddress (or mode code) before another broadcast message
to the same subaddress (or mode code) arrives.
Option 2 for Ping-Pong Mode Broadcast Messages:
The second alternative stores both broadcast and non-broadcast message information in the ping-pong data buffers
A and B. IWA interrupts can signal arrival of any new message. The RT handles broadcast messages just like non-
broadcast messages, except the Message Information Word BCAST bit is asserted to identify broadcast messages
during host buffer servicing. All messages toggle the Control Word DPB bit in message post-processing. For Notice II
compliance, separation of broadcast and non-broadcast data occurs within the host.
Option 2 Setup: At initialization, host negates the NOTICE2 bit in the “Remote Terminal Configuration Register
(0x0017)”. If IWA interrupts are used, the host asserts the descriptor Control Word IWA (Interrupt When Accessed) bit
14 and the corresponding bit is asserted in the “Remote Terminal (RT) Interrupt Enable Register (0x0012)”. Using this
option, the IBR interrupt is probably not used.
The host typically services the ping-pong data buffers A and B whenever a message is transacted. Using the setup
above, this occurs whenever the subaddress IWA interrupt generates an INT interrupt output for the host. The host
must read the Interrupt Log to determine the originating subaddress or mode code. The applicable data buffer is
indicated by the DPB bit in the Receive Control Word. The Message Information Word BCAST bit is asserted if the
message was broadcast.
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