ACT apricot - Page 225

KEYBOARD
In all cases any data in the RAM is destroyed i.e. all record
of
make codes that have been transmitted is lost and the
Keyboard is left in a state where the clock chip is in a
reference signal
output mode, i.e. data line 0 oscillates at
1024 Hz with a 50% duty cycle. While in this state the
Keyboard sends a reset request every 100 ms.
The Keyboard is extracted from this state by sending a
reset
command after which it is in its normal mode of
operation.
If a reset character is received at any other time
all variables will be initialised so that any make codes that
have been transmitted will not have corresponding break
codes transmitted and the initialisation routine will be
called.
An acknowledge character (FB) is transmitted when
the Keyboard is ready for further operation.
The reset character has immediate effect, all characters
that were in the buffer are lost. Synchronisation is achieved
by
using the query command and waiting for the
acknowledge indicating that the buffer is now empty
(provided no more characters have been sent to the
Keyboard in the intervening time) so that a reset can be
sent.
If the command is in the range DOH to D 7H then the LCD
subroutine is called. This controls all direct access to the
LCD, for example the subroutine that displays the time and
date on the LCD reads the contents of the clock IC and then
calls this routine. This in turn calls a subroutine that
actually outputs the data to the LCD and inserts the
appropriate delay to synchronize with the LCD operation. A
record is
kept of the current cursor position, whether the
display is on or off and whether the cursor is on or off in this
routine