ST10R272L - INTERRUPT AND TRAP FUNCTIONS
84/320
can be programmed to one of sixteen interrupt priority levels. Once having been accepted by
the CPU, an interrupt service can only be interrupted by a higher priority service request. For
standard interrupt processing, each of the possible interrupt sources has a dedicated vector
location.
Each interrupt service request is activated by one specific event. The only exceptions are the
two serial channels, where an error interrupt request can be generated by different kinds of
error. However, specific status flags which identify the type of error are implemented in the
serial channels’ control registers.
The ST10R272L provides a vectored interrupt system. In this system, specific vector
locations in the memory space are reserved for the reset, trap, and interrupt service
functions. Whenever a request occurs, the CPU branches to the location that is associated
with the respective interrupt source. This allows direct identification of the source that
caused the request. The only exceptions are the class-B Hardware Traps, which all share
the same interrupt vector. The status flags in the Trap Flag Register (TFR) can then be used
to determine which exception caused the trap. For the special software TRAP instruction,
the vector address is specified by the operand field of the instruction, which is a seven-bit
trap number.
The reserved vector locations build a Jump Table in the low end of the ST10R272L’s address
space (segment 0). The Jump Table is made up of jump instructions that transfer control to
the interrupt or trap service routines which may be located anywhere in the address space.
The entries to the Jump Table are located at the lowest addresses in code segment 0 of the
address space. Each entry occupies 2 words, except for the reset vector and the Hardware
Trap vectors, which occupy 4 or 8 words.
6.1.1
Interrupt sources
The table below lists all sources that are capable of requesting interrupt or PEC services in
the ST10R272L, the associated interrupt vectors, their locations and the associated trap
numbers. It also lists the Interrupt Request Flags mnemonic and the Interrupt Enable flags.
The mnemonics has two parts: a source part and a function part (IR=Interrupt Request flag,
IE=Interrupt Enable flag).
Source of Interrupt or PEC
Service Request
Request
Flag
Enable
Flag
Interrupt
Vector
Vector
Location
Trap
Number
External Interrupt 0
CC8IR
CC8IE
CC8INT
60h
18h
External Interrupt 1
CC9IR
CC9IE
CC9INT
64h
19h
External Interrupt 2
CC10IR
CC10IE
CC10INT
68h
1Ah
Table 13 List of possible interrupt sources, flags, vector and trap numbers