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ORG $100
START LDX #TEXT
JSR PDATA1
JMP CONTRL
TEXT FCB $0D, $0A
FCC /HELLO/
FCB 4
END
- The accumulator and register status after using PDATA1 is as follows:
ACC A Changed during the operation
ACC B UNCHANGED
IXR Contains the memory location of the 04
CHANGE (E088) CHANGE is SWTBUG‘s memory examine and change function. Change
uses a number of other SWTBUG® subroutines.
OUT4HS (E0C8) OUT4HS is used to output a four-digit (16-bit) hexadecimal number onto the
control terminal. The address of the most significant byte to be output should
be loaded into the index register before calling OUT4HS. For example, to
out-put the 16-bit hex number stored in memory locations 1000 and 1001
whose most significant byte is in 1000 while the least significant byte is in
1001 the following sequence should be used:
LDX # $1000
JSR OUT4HS
- If location 1000 contained a hex 3C and 1001 contained a hex 0B, an ASCII,
3C0B would be displayed on the screen when OUT4HS is called. Remember
memory data is handled in hex but must be output as ASCII characters which
have a different hex value than those stored in the computer’s memory. The
registers are affected as follows:
ACC A Changed during the operation
ACC B UNCHANGED
IXR Incremented by two. (1002 in this example)
OUT2HS (E0CA) OUT2HS is similar to OUT4HS, but outputs only two hex characters (one
byte). For example, to display the byte stored at 2008 the following sequence
would be used:
LDX # $2000
JSR OUT2HS
- An ASCII 6C would be output to the control terminal if location 2001
contained a hex 6C. The registers are affected as follows:
ACC A Changed during the operation
ACC B UNCHANGED
IXR Incremented by one. (1001in this example)
OUTS (E0CC) OUTS is a subroutine that outputs one space to the control terminal.
START (E0D0) START is the beginning of a sequence of steps that initialize the system
during power up or reset. First, the stack pointer is set to be A042 and is
stored in SP. Next, an FF is stored in location A943. This sets the interrupt
mask bit in the stack so that when a G command is given the processor will
not respond to interrupts until told to do so. The type of port being used
(ACIA or PIA) is then determined by initializing it as a PIA and looking to see
if this worked. If not, an ACIA is assumed and the proper ACIA initialization
routine, AL2, is selected. The program then goes to CONTRL sequence.