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Last modified on 4 April 2025, at 11:31

RTC

Revision as of 11:31, 4 April 2025 by Phi2x (Talk | contribs) (→‎RTC Registers)

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 Z80 PIO chip to control the HD146818 RTC chip via port A. Do not use Port A as this will affect the RTC operation.
 FBE0h  Dk'tronics Real Time Clock - Z80 PIO Port A Data (HD146818P RTC Data bus)
 FBE1h  Dk'tronics Real Time Clock - Z80 PIO Port B Data, used for external control (General Purpose 8bit I/O Port)
 FBE2h  Dk'tronics Real Time Clock - Z80 PIO Port A Control
 FBE3h  Dk'tronics Real Time Clock - Z80 PIO Port B Control
 FBE8h  Dk'tronics Real Time Clock - Control port for RTC chip (4bit latch) (details unknown)
 Port B is connected directly to a standard 9-way connector on the left of the interface.

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

Registers 00H-09H in BCD mode:

Register Bit Position Function Range
7 6 5 4 3 2 1 0
00H 0 10 Seconds Seconds Seconds 00–59
01H 0 10 Seconds Seconds Seconds Alarm 00–59
02H 0 10 Minutes Minutes Minutes 00–59
03H 0 10 Minutes Minutes Minutes Alarm 00–59
04H AM/PM 0 0 10 Hours Hours Hours 1–12 +AM/PM
0 10 Hours Hours 00–23
05H AM/PM 0 0 10 Hours Hours Hours Alarm 1–12 +AM/PM
0 10 Hours Hours 00–23
06H 0 0 0 0 0 Day Day 01–07
07H 0 0 10 Date Date Date 01–31
08H 0 0 0 10 Months Month Month 01–12
09H 10 Years Year Year 00–99

Registers 00H-09H in binary mode:

Register Bit Position Function Range
7 6 5 4 3 2 1 0
00H 0 0 Seconds Seconds 00–3B
01H 0 0 Seconds Seconds Alarm 00–3B
02H 0 0 Minutes Minutes 00–3B
03H 0 0 Minutes Minutes Alarm 00–3B
04H AM/PM 0 0 0 Hours Hours 01–0C +AM/PM
0 Hours 00–17
05H AM/PM 0 0 0 Hours Hours Alarm 01–0C +AM/PM
0 Hours 00–17
06H 0 0 0 0 0 Day Day 01–07
07H 0 0 0 Date Date 01–1F
08H 0 0 0 0 Month Month 01–0C
09H Year Year 00–63

Control registers: 

 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)

Non-Volatile RAM: 

 0Eh..3Fh battery backed RAM (HD146818, DS1287A, DS12887A and other chips)
 40h..7Fh battery backed RAM (only on DS12887A and newer chip variants)

Other chips