ST20C2 Datasheet, PDF (27/212 Pages) STMicroelectronics – Instruction Set Reference Manual

mnemonic
name
ajw n
adjust workspace
call n
call
cj n
conditional jump
eqc n
equals constant
jn
jump
ldc n
load constant
ldl n
load local
ldlp n
load local pointer
ldnl n
load non-local
ldnlp n
load non-local pointer
stl n
store local
stnl n
store non-local
Table 4.2 Primary instructions
4.1.4 Secondary instructions
The ST20 encodes all other instructions (secondary instructions) indirectly using the
instruction data value.
mnemonic
name
opr
operate
Table 4.3 Operate instruction
The instruction component opr causes the instruction data value to be interpreted as
the operation code of the instruction to be executed. This selects an operation to be
performed on the values held in the integer stack. This allows a further 16 operations
to be encoded in a single byte instruction. However the prefix instr uctions can be used
to extend the instruction data value, allowing any number of operations to be
performed.
Secondary instructions do not have an operand specified b y the encoding, because
the instruction data value has been used to specify the operation.
To ensure that programs are represented as compactly as possible, the operations are
encoded in such a way that the most frequent secondary instructions are represented
without using prefix instr uctions.
4.1.5 Summary of encoding
The encoding mechanism has important consequences.
• Firstly, it simplifies language compilation, b y providing a completely uniform
way of allowing a primary instruction to take an operand of any size up to the
processor word-length.
• Secondly, it allows these operands to be represented in a form independent of
27/212
®