780,781



     whether this new 810 ROM will be made available. For more
     information, see the OS User's Manual.

Locations 780 to 793 ($30C to $319) are for miscellaneous use.
Locations 794 to 831 ($31A to $33F) are handler address tables. To use
these DCBs, the user must provide the required parameters to this
block and then do a machine language JSR to $E453 (58451) for disk
I/O or $E459 (58457; the SIO entry point) for other devices.

780,781        30C,30D        TIMER1
     Initial baud rate timer value.

782            30E            ADDCOR
     Addition correction flag for the baud rate calculations involving
     the timer registers.

783            30F            CASFLG
     Cassette mode when set. Used by SIO to control the program
     flow through shared code. When set to zero, the current
     operation is a standard SIO operation; when non-zero, it is a
     cassette operation.

784,785        310,311        TIMER2
     Final timer value. Timer one and timer two contain reference
     times for the start and end of the fixed bit pattern receive period.
     The first byte of each timer contains the VCOUNT value (54283;
     $D40B), and the second byte contains the current realtime clock
     value from location 20 ($14). The difference between the timer
     values is used in a lookup table to compute the interval for the
     new values for the baud rate passed on to location 750, 751
     ($2EE, $2EF).

786,787        312,313        TEMP1
     Two-byte temporary storage register used by SIO for the
     VCOUNT calculation during baud timer routines. See location
     54283 ($D40B).

788            314            TEMP2
     Temporary storage register.

789            315            TEMP3
     Ditto.

790            316            SAVIO
     Save serial data-in port used to detect, and updated after, each
     bit arrival. Used to retain the state of BIT 4 of location 53775
     ($D20F; serial data-in register).

791            317            TIMFLG
     Time-out flag for baud rate correction, used to define an
     unsuccessful baud rate value. Initially set to one, it is