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Instruction Format

The formats of the instructions for this architecture are shown in the four diagrams below.

First, the instructions that are 32 bits in length which can never affect the condition code bits, as they perform functions such as load and store, or jump:

Second, the instructions that are 32 bits long which perform arithmetic operations, and so have a C bit which will be set to 1 if the instruction is to affect the condition code bits:

Note that some of these instructions may have immediate values; in that case, they will take up more than 32 bits of space, but the immediate value is, for purposes of this classification, not considered part of the instruction itself.

Third, the instructions that are longer than 32 bits, and so have a pSupp field to point to the extra portion of the instruction, and have a C bit because they perform a calculation:

And finally, fourth are the instructions that are longer than 32 bits but do not have a C bit:

These diagrams show the instructions which occupy a full 32-bit instruction slot. The 16-bit instructions which the header format can call for in some instruction slots will be described on the next page.

In many cases, the instructions will be longer than 32 bits.

When an instruction contains a pSupp field, in Mode 2 and Mode 3 that field points to one of the sixteen extents of 16 bits into which the 256-bit instruction block may be divided. Such instructions cannot be used in Mode 0; in Normal Prefix Mode (Mode 2), although that field may be present, the bits within it are not used, and so the field must contain all zeroes, as the instruction prefix indicates the length, and, if necessary, the position, of the additional portions of an instruction. In Enhanced Prefix Mode (Mode 3), in the additional instruction format made available in that mode, the field contains the length, in units of 16 bits, of the supplementary portion of the instruction. And in both Hybrid CISC Mode (Mode 5) and Extended Hybrid Mode (Mode 6) the pSupp field contains the total length of the instruction, in units of 16 bits, minus two, so it contains both the length of the supplementary portion of the instruction and that of any immediate present combined.

In the case where an instruction has a pSupp field, following the illustration of the format of the 32-bit part of the instruction, after a gap, the format of the supplementary portion of that instruction is shown on the same line.

Note that, in several cases, including the format shown on the first line, the first two bits of an opcode field contain dotted boxes. This indicates that the format in question is distinguished from following ones by the fact that the first two bits of that opcode field may not both be ones.

When an instruction contains one or more pImm fields, in Mode 2 and Mode 3 each such field points to one of the thirty-two bytes composing a 256-bit instruction block. Such instructions cannot be used in Mode 0: in Mode 2, the values within these fields are not used, and the fields present must contain all zeroes; the required information to locate, and determine the length of, each immediate value used in the instruction is within the 16-bit instruction prefix. In Mode 3, in the additional instruction format made available in that mode, each pImm field is a pointer to the last byte (the one with the least significant bits in it, the one located at the highest memory address) of the immediate value to which it refers, relative to the beginning of the instruction.

This additional portion of an instruction, the immediate value or values that may be associated with it, is not shown in the diagram; it consists of immediate data, and is thus in the big-endian version of the normal data format for the appropriate data type.


Note that the instructions in the diagrams above are ordered.

000000 000000 to 164377 177777  Instructions without a C bit and without a pSupp field
164400 ------ to 167777 ------  Prefixes
170000 000000 to 171777 177777  Instructions with a C bit and without a pSupp field
172000 000000 to 172037 177777  Instructions with a C bit and with a pSupp field
172040 000000 to 177777 177777  Instructions without a C bit and with a pSupp field

Instructions are not, however, in strict numerical order. The C bit and the pSupp field are ignored in ordering instructions, and, thus, since bits past those bits are used where a C bit is present, in the instructions without a C bit that come afterwards, the bit in that position is treated as less significant than bits 5 and 10 that come after it.

The area from 164400 to 1677777 is reserved for the 16-bit instruction prefixes used in Mode 2 and Mode 3.

Instructions within each of the two blocks of instructions with a pSupp field are also further ordered by the length of the supplementary field, with length increasing as one proceeds ahead through the list.

Instructions within each of the two blocks of instructions with a C bit are additionally ordered in that the instructions with fields that may be switched between being register fields or pImm fields are placed at the beginning of those blocks, and the instruction format with two such fields is placed before that with only one such field.


As for how data values are stored:

Signed integer values are stored in binary two's complement format.


The standard types of floating-point numbers used by this architecture are shown below:

The 32-bit and 64-bit floating point formats correspond to that used in the IEEE 754 specification. A similar 48-bit floating-point format is added.

The 80-bit floating-point format, except for being stored in big-endian order, is that found on popular microcomputers, and the 128-bit format is the same format except for the significand being larger.


Note that the numbers for some of the instruction formats are circled.

These are the instruction formats that may appear in code which may be executed in Mode 0. (At one time, the term unblocked code was used for such code, but code for execution in modes 2, 3, 4 and 5 is also not organized in instruction blocks.)

These instruction formats may not have either pSupp fields or pImm fields; however, instructions that may have pImm fields are allowed, but only when those fields are used as register fields instead.


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