ACU Real Time Clock, DIY from magazine [[Amstrad Computer User|Amstrad User]], April 85.
* The RTC chip doesn't include a Year register (aside from the leap-year shift register, but it can span only 4 years, and it is write-only). == Technical == Uses a [[Z80 PIO]], MM58174 RTC, 6116 (2Kx8bit SRAM), 4040 (12bit counter for sequential SRAM addressing), and 32.768kHz Crystal (for the RTC). Both RTC and RAM are backed by rechargeable 3.6V NiCad battery. Used I/O Ports are (with only A10,A4,A3 decoded): FBE7h ACU Real Time Clock [[Z80 PIO]] Data In/Out Port A Bit7..4 SRAM Data7..4 Bit3..0 SRAM Data3..0 and 4bit RTC Data FBEFh ACU Real Time Clock [[Z80 PIO]] Data In/Out Port B Bit7 SRAM /CS and /OE (0=Select) Bit6 RTC /CS (0=Select) Bit5 RTC /RD (0=Read) Bit4 RTC /WR (0=Write) Bit3 RTC Address A3 and SRAM /WE (0=Write) Bit2 RTC Address A2 and SRAM Address Counter RST (1=Reset, 0=Active) Bit1 RTC Address A1 Bit0 RTC Address A0 and SRAM Address Counter /CLK (1-to-0=Increment) FBF7h ACU Real Time Clock [[Z80 PIO]] Configure Port A FBFFh ACU Real Time Clock [[Z80 PIO]] Configure Port BThe 4bit RTC Registers are: 0 Not used / Test (W) 1 Seconds 1/10s Fraction (0..9) (R) 2 Seconds LSB (0..9) (R) 3 Seconds MSB (0..5) (R) 4 Minutes LSB (0..9) (R/W) 5 Minutes MSB (0..5) (R/W) 6 Hours LSB (0..9) (R/W) 7 Hours MSB (0..2) (R/W) 8 Day LSB (0..9) (R/W) 9 Day MSB (0..3) (R/W) A Day of Week (1..7) (R/W) B Month LSB (0..9) (R/W) C Month MSB (0..1) (R/W) D Leap Year Shift Register (W) E Stop/Start (0=Stop and set Seconds to 00.0, 1=Start) (W) F Interrupt (R/W)Registers 1..C are BCD (range 0..9), a value of 0Fh in these registers indicates Failure (this may happen if the time changed while reading - if that happens, restart reading ALL time registers). == Article == <gallerycaption="Part 1 - RTC DIY Hardware (ACU April 1985)">
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Observe that the part number, MM58147, in the headline is wrong (it's meant to be MM58174).
<gallery caption="Part 2 - Software for the RTC (ACU May 1985)">
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[[Category:Peripherals]] [[Category:DIY]]