522,523



     or the console buttons. Console buttons never generate an
     interrupt unless one is specifically user-written. VKEYBD can be
     used to process the key code before it undergoes conversion to
     ATASCII form. Initialized to 65470 ($FFBE) which is the OS
     keyboard IRQ routine.

522,523        20A,20B        VSERIN
     POKEY serial I/O bus receive data ready interrupt vector,
     initialized to 60177 ($EB11), which is the OS code to place a byte
     from the serial input port into a buffer. Called INTRVEC by DOS,
     it is used as an interrupt vector location for an SIO patch. DOS
     changes this vector to 6691 ($1A23), the start of the DOS
     interrupt ready service routine. IRQ.

524,525        20C,20D        VSEROR
     POKEY serial I/O transmit ready interrupt vector, initialized to
     60048 (EA90), which is the OS code to provide the next byte in a
     buffer to the serial output port. DOS changes this vector to 6630
     ($19E6), the start of the DOS output needed interrupt routine.
     IRQ.

526,527        20E,20F        VSEROC
     POKEY serial bus transmit complete interrupt vector, initialized
     to 60113 ($EAD1), which sets a transmission done flag after the
     checksum byte is sent. IRQ.

     SIO uses the three last interrupts to control serial bus
     communication with the serial bus devices. During serial bus
     communication, all program execution is halted. The actual
     serial I/O is interrupt driven; POKEY waits and watches for a flag
     to be set when the requested I/O operation is completed. During
     this wait, POKEY is sending or receiving bits along the seriai
     bus. When the entire byte has been transmitted (or received), the
     output needed (VSEROR) or the input ready (VSERIN) IRQ is
     generated according to the direction of the data flow. This causes
     the next byte to be processed until the entire buffer has been sent
     or is full, and a flag for "transmission done" is set. At this point,
     SIO exits back to the calling routine. You can see that SIO wastes
     time waiting for POKEY to send or receive the information on the
     bus.

528,529        210,211        VTIMR1
     POKEY timer one interrupt vector, initialized to 59314 ($E7B2),
     which is a PLA, RTI instruction sequence. Timer interrupts are
     established when the POKEY timer AUDF1 (53760; $D200)
     counts down to zero. Values in the AUDF registers are loaded
     into STIMER at 53769 ($D209). IRQ.