SYMBiFACE II:Realtime clock

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This is the documentation about the realtime clock of the SYMBiFACE II expansion card.


  • #FD15 (write only) register select
  • #FD14 (read/write) read from or write into selected register


Number  Content             Values
#00     actual second       00-59 (bcd or binary)
#01     alarm second        00-59 (bcd or binary)
#02     actual minute       00-59 (bcd or binary)
#03     alarm minute        00-59 (bcd or binary)
#04     actual hour         00-23 (bcd or binary)
#05     alarm hour          00-23 (bcd or binary)
#06     day of the week     ??
#07     day of the month    01-31 (bcd or binary)
#08     month               01-12 (bcd or binary)
#09     year                00-99 (bcd or binary)
#0A     status A            see below
#0B     status B            see below
#0C     status C            see below
#0D     status D            see below
#32     millenium           19 or 20 (bcd or binary)
#??     memory              all other registers can be freely used as persistent memory

Status registers

  • Status A
bit0-3  [not used] interrupt frequency
bit4-6  time frequency (must be 010; if not, set it to this value, otherwise the RTC will not work correctly)
bit7    1 = time is being updated at the moment, so don't read it!
  • Status B
bit0    1 = take summer time into account
bit1    0 = 12 hours time format, 1 = 24 hours time format
bit2    0 = all values in BCD format, 1 = all values in binary format
bit3    1 = [not used] activate rectangle generator
bit4    1 = [not used] generate interrupt after time update
bit5    1 = [not used] generate interrupt if alarm
bit6    1 = [not used] generate periodic interrupt (see status A, bit0-3)
bit7    1 = stop time update; set this, during you update the time and reset it after the update!
  • Status C
bit4    1 = [not used] interrupt has been generated because of time update (see status B, bit4)
bit5    1 = [not used] interrupt has been generated because of alarm (see status B, bit5)
bit6    1 = [not used] interrupt has been generated because of periodic (see status B, bit6)
  • Status D
bit7    0 = battery is nearly empty, please charge or replace

See also