ST20-C1 STMICROELECTRONICS [STMicroelectronics], ST20-C1 Datasheet - Page 27

• Manufacturer Part Number: ST20-C1
• Description: Instruction Set Reference Manual
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

The mnemonics and names for the primary instructions are listed in Table 3.5.
3.4.4
The ST20 encodes all other instructions, known as secondary instructions, indirectly
using the instruction data value.
The function code 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 evaluation stack, so that a further 16 operations
can be encoded in a single byte instruction. The pfix instruction component can be
used to extend the instruction data value, allowing any number of operations to be
encoded.
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 frequently used secondary instructions are
represented without using prefix instructions.
For example, the instruction add is encoded by:
The instruction and is encoded by:
Secondary instructions
opr 4
opr F9
adc n
ajw n
fcall n
cj n
eqc n
j n
ldc n
ldl n
ldlp n
ldnl n
ldnlp n
stl n
stnl n
opr n
mnemonic
mnemonic
Table 3.5 Primary instructions
Table 3.6 Operate instruction
add constant
adjust work space
function call
conditional jump
equals constant
jump
load constant
load local
load local pointer
load non-local
load non-local pointer
store local
store non-local
operate
name
name
3 Architecture
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