Difference between revisions of "RTC"

Revision as of 04:16, 2 April 2025

Real Time Clock (RTC)

PC compatible RTC chip

Usage in CPCs

Usage in SYMBiFACE II:Realtime clock:

 Uses a Dallas DS12887A RTC chip, mapped to ports:
 FD14h SYMBiFACE II Real Time Clock - DS12887A RTC Data  (R/W)
 FD15h SYMBiFACE II Real Time Clock - DS12887A RTC Index (W)

Usage in Dk'tronics Real Time Clock:

 Uses a HD146818 chip.
 Details on I/O addresses are unknown.

Usage in Aleste 520EX - I/O Ports:

 Uses a russian KR512WI1 chip (which is, according to the Aleste's 
 Manual) compatible to western MC146818 chips. 
 Connects to a 32.768kHz crystal.
 Connects to the PPI:
   PPI Port A.Bit0-7 = Data bus
   PPI Port C.Bit0   = Read/Write   (0=Write, 1=Read)
   PPI Port C.Bit1   = Index Access (0=No, 1=Access)
   PPI Port C.Bit2   = Data Access  (0=No, 1=Access)
 In the Aleste's Ext Port, the RTC must be enabled, and PSG and
 8253 must be disabled.

RTC Registers

 00h  Second       (00..59) ;\
 01h  Alarm second (00..59) ; these ten registers can be BCD or Binary
 02h  Minute       (00..59) ; (see Control B, Bit2=DM)
 03h  Alarm minute (00..59) ;
 04h  Hour         (00..23) ;  ;\in 24hour mode:
 05h  Alarm hour   (00..23) ;  ;/bit7=PM
 06h  Day of week  (01..07) ;
 07h  Day          (01..31) ;
 08h  Month        (01..12) ;
 09h  Year         (00..99) ;/
 0Ah  Control A
       7   UIP Update in Progress (0=Stable in next 244us, 1=Time changes) (R)
       6-4 DV  Oscillator control (must be 2 for normal operation)
       3-0 RS  Rate Selector for IRQ pin (not used by SYMBiFACE II)
 0Bh  Control B
       7   SET  Stop clock, to be set/cleared before/after writing to [0h..9h]
       6   PIE  Periodic Interrupt Enable (see Control A, RS)
       5   AIE  Alarm Interrupt Enable
       4   UIE  Update-Ended Interrupt Enable (aka Seconds Interrupt)
       3   SQWE Square-Wave Enable (see Control A, RS)
       2   DM   Data Mode for [00h..09h] (0=BCD, 1=Binary)
       1   24H  24-Hour Mode             (0=12h with AM/PM, 1=24h)
       0   DSE  Daylight Saving Enable   (0=No, 1=Uses hardcoded timezone)
 0Ch  Control C (read-only, automatically reset to zero after reading)
       7   IRQF Interrupt Request Flag (1 on PIE,AIE,UIE, 0 after read) (R)
       6   PF   Periodic Interrupt Flag     (see Control A, RS)         (R)
       5   AF   Alarm Interrupt Enable Flag                             (R)
       4   UF   Update-Ended Interrupt Flag (aka Seconds Interrupt)     (R)
       3-0 0    Reserved (zero)
 0Dh  Control D (read-only)
       7   VRT  Valid RAM and Time (1=Okay, 0=Battery Low)              (R)
       6-0 0    Reserved (zero)
 0Eh..3Fh battery backed RAM (HD146818, DS1287A, and other chips)
 40h..7Fh battery backed RAM (DS12887A, newer chip variants only)
 80h..FFh reserved

Other chips

• ACU Real Time Clock (DIY)
• Dobbertin Smart Watch
• URTC-8 Universal RTC for Z80 computers
• Nova (M48T35Y-70MH1F chip)