w65c816s Western Design Center, Inc., w65c816s Datasheet - Page 50

• Manufacturer Part Number: w65c816s
• Description: W65c816s 8/16?bit Microprocessor
• Manufacturer: Western Design Center, Inc.

6.3.4 Comment Field
The comment field may start no sooner than one space after the operation code field or
operand field depending on instruction type.
6.3.3.3 Note that the operand does not determine whether or not immediate address loads one
or two bytes, this is determined by the setting of the status register. This forces the requirement
for a directive or directives that tell the assembler to generate one or two bytes of space for
immediate loads. The directives provided shall allow separate settings for the accumulator and
index registers.
6.3.3.4 The assembler shall use the <, >, and ^ characters after the # character in immediate
address to specify which byte or bytes will be selected from the value of the operand. Any
calculations in the operand must be performed before the byte selection takes place. Table 7-3
defines the action taken by each operand by showing the effect of the operator on an address.
The column that shows a two byte immediate value show the bytes in the order in which they
appear in memory. The coding of the operand is for an assembler which uses 32-bit address
calculations, showing the way that the address should be reduced to a 24-bit value.
6.3.3.5 In any location in an operand where an address, or expression resulting in an address, can
be coded, the assembler shall recognize the prefix characters <, |, and >, which force one byte
(direct page), two byte (absolute) or three byte (long absolute) addressing. In cases where the
addressing modes is not forced, the assembler shall assume that the address is two bytes unless
the assembler is able to determine the type of addressing required by context, in which case that
addressing mode will be used. Addresses shall be truncated without error in an addressing mode is
forced which does not require the entire value of the address. For example, LDA $0203 and LDA
|$010203 are completely equivalent.
addressing cannot be determined from context, the assembler shall assume that a two byte
address is to be used. If an instruction does not have a short addressing mode (as in LDA< which
has no direct page indexed by Y) and a short address is used in the operand, the assembler shall
automatically extend the address by padding the most significant bytes with zeroes in order to
extend the address to the length needed. As with immediate address, any expression evaluation
shall take place before the address is selected; thus, the address selection character is only used
once, before the address of expression.
6.3.3.6 The (!) exclamation point character should be supported as an alternative to the |
(vertical bar).
6.3.3.7 A long indirect address is indicated in the operand field of an instruction field of an
instruction by surrounding the direct page address where the indirect address is found by square
brackets; direct page addresses which contain 16-bit addresses are indicated by being
surrounded by parentheses.
#$01020304
#<$01020304
#>$01020304
#^$01020304
Table 6-3 Byte Selection Operator
Operand
If the addressing mode is not forced, and the type of
One Byte
Result
04
04
03
02
Two Byte
04
04
03
02
Result
03
03
02
01
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