This is the documentation about the '''realtime clock''' of the [[SYMBiFACE II]] expansion card.
SYMBiFACE II uses a Dallas DS12887A RTC chip. [https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/real-time-clock-board/msg249380/#msg249380 Source]
This chip is a modernized version of the MC146818, the original RTC chip used in the IBM PC/AT. It includes a built-in battery and crystal. It is a [[PC compatible RTC chip]] and is programmed in the same way.
It has 14 bytes of registers and 114 bytes of battery-backed static RAM. Century register doesn't exist on this particular model. The chip also provides time-of-day alarm, three maskable interrupts with a common interrupt output, and a programmable square wave output.
It has hardcoded daylight saving adjustment, 24-hour and 12-hour format modes, binary and BCD format modes.
== Ports ==
* #FD15 (read write only) register select
* #FD14 (read/write) read from or write into selected register
== Registers ==
<pre>
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 ??01-07#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 from #0E to #7F can be freely used as persistent memory
</pre>
Note: Register B, Bit 2 allows to select BCD or Binary mode for registers 0..9
Note 1: In the discmag [[Future View IV]] a proposal is given how to use the non volatile RAM of the SYMBiFACE II and the CPC-Booster+.
== Status registers ==
* '''Status A'''
<pre>
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 beeing being updated at the moment, so don't read it!
</pre>
* '''Status B'''
<pre>
bit0 1 = take summer time into account
* '''Status C'''
<pre>
bit4 1 = [not used] interrupt has been generated because of time update (see status B, bit4)
* '''Status D'''
<pre>
bit7 0 = battery is nearly empty, please charge or replace
</pre>
== Software ==
The RTC of the SYMBiFACE II is supported by [[FutureOS]], [[SymbOS]], [[HDCPM]].
== See also ==
* [[Media:DS12887 RTC datasheet.pdf|Dallas DS12887A datasheet]]
* [[SYMBiFACE II:RTC routines|Routines for using the RTC]]
* [[Programming:SYMBiFACE_II|SYMBiFACE II documentations]]
[[Category:FutureOS]]
[[Category:Hardware]]
[[Category:Peripherals]]
[[Category:Programming]]