HI-6136_16 Datasheet, PDF (43/206 Pages) Holt Integrated Circuits – Compact Multi-Terminal Device with SPI Host Interface

HI-6136
Bit No.
1
Mnemonic
DPBTOFF
Function
Bit 1 DPBTOFF disables ping pong DPB pointer toggle when the received valid command
is illegal, or when a message occurs with Busy status.
When using ping pong buffers, the DPB buffer pointer never toggles for valid, legal
messages ending in error. Setting DPBTOFF = 1 also disables ping pong DPB pointer
toggle when the received valid command is illegal, or when a message occurs with Busy
status.
For RT subaddresses using ping pong data buffers (see “Ping-Pong Data Buffering” on
page 120), the device alternates message data storage between Data Buffer A and Data
Buffer B, on a message-by-message basis. The Descriptor Table Control Word DPB bit
10 indicates the data buffer to be used by the next-occurring message to this subaddress
(see Section “14.4. Descriptor Table” on page 95). When the DPB bit is logic 0, the next
message uses Data Buffer A; when DPB is logic 1, the next message uses Data Buffer B.
Set DPBTOFF = 1 to prevent toggle of the Control Word DPB bit for Illegal or RT Busy
messages, as well as valid, legal messages ending in error. The DPB pointer therefore
remains static until the next successful message is received, which overwrites the
Message Information Word and Time Tag Word in the current ping pong buffer location.
Note that receive and transmit subaddresses may have both legal and illegal word counts,
dictated by the Command Illegalization Table. For such subaddresses, DPB toggle only
occurs when a supported legal word count message is transacted.
When the DPBTOFF option bit is set to modify behavior for ping pong buffers, DPB
toggle is disabled for valid messages that are illegal, or legal messages resulting in RT
Busy or Message Error status. Important note: message data words in the “next-used”
(designated active) buffer are NOT altered for incomplete (illegal, Message Error or RT
Busy) messages. However the buffer Message Information and Time Tag Words are
updated in that message data buffer so the host can detect when such messages
occur. Bits 10:8 in the buffer Message Information Word indicate Message Error, Busy
and/or Illegal status. When any of these 3 bits are set, the accompanying data should
always be disregarded (whether or not the DPBTOFF option is used).
To maintain data integrity, the primary benefit of DPBTOFF = 1 is that the complemented
DPB pointer always indicates the last-transacted “good” data set. For example if DPB is
logic 0, the last successful message used Data Buffer B.
The default condition after power-on reset in register 0x4D contains 0x0000. Thus
configuration bit DPBTOFF is logic-0. For this case, the Control Word DPB bit toggles
after completion of error-free messages (expected), but also illegal commands and
messages resulting in Message Error or Busy status.
HOLT INTEGRATED CIRCUITS
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