21.4.11.1 Message format

Each message comprises an instruction followed by one or more byte operands. The instruction is always sent by the external programmer. Depending on the instruction all the following operands are sent either by the external programmer or by the TPI.

The messages can be categorized in two types based on the instruction, as follows:
  • Write messages. A write message is a request to write data. The write message is sent entirely by the external programmer. This message type is used with the SSTCS, SST, STPR, SOUT and SKEY instructions.
  • Read messages. A read message is a request to read data. The TPI reacts to the request by sending the byte operands. This message type is used with the SLDCS, SLD and SIN instructions.

All the instructions except the SKEY instruction require the instruction to be followed by one byte operand. The SKEY instruction requires 8 byte operands. For more information, see the TPI instruction set.