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INTEL 186 EB/EC EVALUATION BOARD USER’S MANUAL
6-2
6.2 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. The RISM is 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 internal state structure of the RISM was kept as simple as possible. There are only three
internal flags that can change the way that the RISM deals with a character sent by the host.
6.3 RECEIVING DATA FROM THE HOST
When the RISM receives a character from the host, its first task is to determine whether the
character represents a command or data. When the character is less than 32 (decimal), it is
assumed to be a command. When the character is more than 32 (decimal), it is assumed to be data.
When the host needs to send a data byte that has a value less than 32, it first must issue a
SET_DATA_FLAG command. When the DATA_FLAG is set, the next character received by the
RISM is interpreted as data (even if it is less than 32), and the DATA_FLAG is cleared. Once the
RISM determines 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
RISM_DATA register. The data shifted out of the upper byte of the RISM_DATA register is
discarded.
6.4 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 by eight bits. As part of this command, the RISM
increments its RISM_ADDR register. The RISM transmits data only in response to a
TRANSMIT command, never on its own initiative or even in response to other commands from
the host.
6.5 RISM COMMANDS
This section details the operation of each of the commands sent to the RISM.