58460



     SIO first sends a command frame to the device, consisting of five
     bytes: the device ID, the command BYTE, two auxiliary bytes for
     device-specific information, then a checksum (which is the sum
     of the first four bytes). If the device acknowledges this frame, it is
     followed, if necessary, by the data frame of a fixed number of
     bytes depending on the device record size, plus a checksum
     byte. Initialized to 59737 ($E959).

58460          E45C           SETVBV
     Set system timers during the VBLANK routine. Uses the 6502 X
     register for the MSB of vector/times, Y for the LSB and A for the
     number of the vector to hack (change). SETVBV insures that both
     bytes of the vector addressed will be updated while VBLANK is
     enabled. You can JSR here when creating your own timer
     routines. See COMPUTE!, November 1981, for an application.
     Initialized to 59666 ($E912) old ROMs, 59629 ($E8ED) new
     ROMs.

58463          E45F           SYSVBV
     Stage one VBLANK calculations entry. It performs the
     processing of a VBLANK interrupt. Contains JMP instruction for
     the vector in the next two addresses (58464, 58465; $E460,
     $E461). This is the address normally found in VVBLKI (546, 547;
     $222, $223). It is initialized to 59345 ($E7D1), which is the
     VBLANK routine entry. Initialized to 59345 ($E7D1) old ROMs,
     59310 ($E7AE) new ROMs.

58466          E462           XITVBV
     Exit from the VBLANK routine, entry point. Contains JMP to the
     address stored in next two locations (58467, 58468; $E463,
     $E464). This is the address normally found in VVBLKD (548, 549;
     $224, $225). Initialized to 59710 ($E93E), which is the VBLANK
     exit routine. It is used to restore the computer to its pre-interrupt
     state and to resume normal processing. Initialized to 59710
     ($E93E) old ROMs, 59653 ($E905) new ROMs.

58469          E465           SIOINV
     SIO utility initialization, OS use only.

58472          E468           SENDEV
     Send enable routine, OS use only.

58475          E46B           INTINV
     Interrupt handler initialization, OS use only.

58478          E46E           CIOINV
     CIO utility initialization, OS use only.

58481          E471           BLKBDV
     Blackboard mode entry. Blackboard mode is the "ATARI MEMO