Commodore PET User Manual page 426

So 24 is to be stored at location 134 (Iow byte). and 28 is to be stored at location
135 (high byte). The following instructions can be used:
10 AL=PEEK(134):AH=PEEK(135):
20 POKE 132.24:POKE 135.28:
REM SAVE CURRENT POINTER
REM TOP OF CORE NOW = 7192
1~1et
POKE 134 .. AL: POKE 135 .. AH:
1113 Erm
REM RE3TORE POINTER
Chapter 6: USR
Since the accumulator is maintained in different system locations on the old
ROMs, the accumulator description will read as follows:
The parameter value is passed to the USR subroutine in system locations
that function as a floating point accumulator (FAC) for ail functions. The FAC
resides in six bytes fram memory locations 176 to 181 (8°16-8516). The FAC has
the following format:
O=positive
-1 =negative
(FAC
ating
nt)
178 179 180 181
Fraction
Flo
1
1
Poi
11
Sign
l
Exponent
f
Memory location: 176 177
Like floating point variables. the exponent is stored in excess 128 format. and the
fraction is normalized with the high-order bit of byte 177 (the high-order byte of
the fraction) set to 1. The difference between this format and the variable format
is that the high-order 1 bit is present in byte 177 of the FAC. An extra byte (181) is
used to hold the sign of the fraction. (This is done for ease of manipulation by the
functions that use the FAC).
1. PET User Notes. Volume 1. Issue 6. Sept.-Oct. 1978. pg. 14.
"Cassette File Usage Summary" by Jim Butterlield.
2. Best 01 the PET GAZETTE. pg. 38
"On Data Files:", by Michael Richter.
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