Aim MIL-STD-1553 - Page 255

MIL-STD-1553 Reference Manual
241
Chapter 7 – Bus Controller Functions
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All API functions return API_OK if no error occurred. If the return value is not equal
to API_OK the function ApiGetErrorDescription can be used to obtain an error
description.
Notice: The Target Software implements the following Service Request / Vector Word handling in BC
mode: When the BC detects a service request from a RT (Service Request Bit set in RT Status
response) a Transmit Vector Word Mode Code command is transferred to the requesting RT. As
response on the mode code the RT transmits a Vector Word to the BC, which is interpreted and handled
by the BC following the description given in the ‘AVS Databus Usage Report R-J-403-V-1209 Par. 7.2.’.
The Vector Word comprises a 4-bit identification code informing the BC about the service request reason
and specifying the action the BC has to perform. Besides the identification code, the vector word defines
the RT address and the Subaddress / HS Message Identifier of the service requesting RT.
Bit 15..12
Bit 11..7
Bit 6..0
Id – Code
RT-Address
Subaddress / MID
The Vector Word Id – Codes requiring BC transactions are handled by the Target Software as follows:
Request Single RX/TX (1000/1001):
The related BC transaction is executed once immediately (acyclic) after receipt and decoding of the
vector word.
Request Multiple RX/TX (1010/1011):
The related BC transaction is enabled by appending it to the end of the current BC minor frame (Cyclic
execution until disabled).
Delete RX/TX (1100/1101):
The related BC transaction is disabled by deleting it from the end of the related BC minor frame. Re-
enabling requires receipt of the corresponding vector word code (Request Multiple RX/TX 1010/1011).
Only BC transactions which have been enabled by a previous ‘Request Multiple RX/TX’ vector word can
be disabled.
BC transfers which shall be used as ‘vector word driven’ transactions have to be marked with the
ApiCmdBCXferDef command (refer to parameter ‘sxh’) accordingly. Only BC-RT and RT-BC transfer
types can be defined to be ‘vector word driven transactions’.