special logic circuits
-- Used for status of devices at SCSI bus initialization
(including the status of the Apple II SCSI card itself)
4. R... issues calls to the microprocessor to give it the status of the
external SCSI devices and all... operation
1. Commands supported: STATUS, READ BLOCK, WRITE BLOCK, FORMAT,
CO
rm, but I've never made
it very clear what their status was. Partly this is because
the previous environ... on the serial port. Pup ANDs
the contents of the status register with the cd-bit, and if
the result is n
HELPS.
THE 6502 PROCESSOR HAS WHAT IS CALLED A STATUS REGISTER, "P". MOST OF
THE 6502 CPU INSTRUCTIONS AFFECT THE STATUS REGISTER P. FOR EXAMPLE,
IF WE HAD JUST EXECUTED ... PROGRAM COUNTER, STACK POINTER, AND THE PROCESSOR
STATUS REGISTER P.
IF WE WERE TO TALK ABOUT THE APPLE ... ILL PRESENT IN THE ACCUMULATOR.)
THE PROCESSOR STATUS REGISTER P IS RATHER LIKE A BLACKBOARD WHERE WE
M
ROTE DOS, EMPLOYED A SIMPLE WA Y OF RECORDING THE STATUS (FULL OR
EMPTY) OF EVERY SINGLE SECTOR ON THE DIS... S SEEMINGLY MEANINGLESS D ATA ABOUT EACH SECTOR'S STATUS BUT
REMEMBER THAT ALL HEX BYTES ARE COMPOSED OF 8
THE INFORMATION IN BETWEEN THESE LINES IS THE STATUS INFORMATION AND
INFORMS YOU OF SUCH THINGS AS C... G
I,J,K OR M, AND WATCH THE ADDR INDICATOR IN THE STATUS LINE. IT WILL TELL YOU
EXACTLY WHAT MEMORY ADDRE... CREMENT AND DECREMENT THE
TRACK NUMBER IN THE STATUS LINE. PRESSING 'R' WILL CAUSE DRIVE ONE TO READ
THE DATA FROM THE TRACK INDICATED IN THE STATUS LINE INTO MEMORY. THE BYTES
ON THE SCREEN WILL
AMS
5. THE P REGISTER- KEEPS TRACK OF THE SYSTEM STATUS. IT IS DIVIDED INTO BITS, LIKE THIS:
7 6... LAST RESULT DID NOT OVERFLOW
*. UNUSED
B. BREAK STATUS-1 AFTER A BRK COMMAND
D. DECIMAL MODE-0 AFTER CL... R, ROL, ROR
5. COMPARE:CMP, CPX, CPY
6. STATUS:SEC, SED, SEI, CLC, CLV,, CLD, CLI
7. BRANCH
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Apple //e Soft Switch, Status, and other I/O locations
\-----------------------... SON Select high resolution graphics
SOFT SWITCH STATUS FLAGS
$C010 R7 AKD 1=key pressed 0=keys free