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EV80C196KB Microcontroller Evaluation Board User's Manual
RISM Structure
The RISM resides in the target system and provides the interface between the target
system and the user interface which resides in the host system. A design goal of
the RISM was to keep it compact and simple. This serves two purposes:
1. The RISM can reside in a user's system with minimal impact on available
memory
2. The RISM is easy to port into the target's environment.
The goals were met by keeping the internal state structure of the RISM as simple as
possible. There are only three internal flags which can change the way that the
RISM deals with a character sent by the host.
DLE-FLAG: If this flag is set then the next received character is assumed to
be a data byte as opposed to a command byte.
RUN-FLAG: This flag is set if the target is running user code. It can modify
the operation of some of the RISM commands.
TRAP-FLAG: This flag is set if the user code has been halted because it
executed a TRAP instruction. The TRAP-FLAG is cleared whenever the
RISM starts the execution of user code.
Receiving Data from the Host
When the RISM receives a character from the host its first task is to determine if it
represents a command or data. If the character is less than 32 (decimal) then it is
assumed to be a command, if not then it is taken to be data. If the host needs to
send a data byte which has a value less than 32 then it first must issue a SET-DLE
command. If the DLE-FLAG is set then the next character received by the RISM will
be interpreted as data (even if it is less than 32) and then the DLE-FLAG will be
cleared. Once the RISM has determined that the received character is a data byte it
processes it by shifting the 32-bit RISM-DATA register left eight places and then
placing the data byte in the lower byte of the RISfv'l-DATA register. The data shifted
out of the upper byte of the RISM-DATA register IS discarded.
Sending Data to the Host
When the host expects data to be returned from the RISM it sends a TRANSMIT
command byte and waits for a response. The RISM transmits the lower byte of the
32-bit RISM-DATA register and right shifts the RISM-DATA register right by eight
bits. As part of this command the RISM increments Its RISM-ADDR register. The
RISM only transmits data in response to an TRANSMIT command, never on its own
initiative or even in response to other commands from the host.
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