Filter
Top Products
6-22 Raster Graphics EN
The sign of the number in the control byte identifies whether the byte
or bytes that follow represent a literal pattern or byte to be repeated. A
positive number (1 to 127) indicates that the bytes are literal. A
negative number (-1 to -127), represented by the twos complement,
indicates a repeated byte. The value of the number, if positive (literal),
identifies the number of pattern bytes which follow the control byte; if
negative (repeated), it identifies the number of times to repeat the
following byte. A pattern byte may be repeated up to 127 times; or up
to 127 literal bytes may follow the control byte.
As mentioned, for a byte to be repeated, the control byte must be a
negative value as represented by the twos complement. For example,
to repeat a pattern three times would require the twos complement of
the number 3. The twos complement is computed as follows. The
binary of 3 is 00000011. Complement each bit to get 11111100, then
add one to this value to produce 11111101, the twos complement.
The decimal value of this number, 253, used in the control byte,
produces a repetition of 3 bytes for a total of 4 occurrences of the
pattern.
The range of numbers for the control byte is shown below.
Literal Pattern Values
# of Bytes Binary value Decimal value
1
to
127
0000 0000
to
0111 1111
1
to
127
No Operation Value
NOP value Binary value Decimal value
128 (-128) 1000 0000 128
Repeated Pattern
Values
# of Repetitions Binary value* Decimal value
1 (-1)
to
127 (-127)
1111 1111
to
1000 0001
255
to
129
* These negative values are represented by taking the twos complement of the value
of the number.