View source for ACU Real Time Clock (DIY)

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 B
The 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 ==

<gallery caption="Part 1 - RTC DIY Hardware (ACU April 1985)">
image:Amstrad Computer User8504 078.jpg
image:Amstrad Computer User8504 079.jpg
image:Amstrad Computer User8504 080.jpg
image:Amstrad Computer User8504 081.jpg
</gallery>

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)">
image:ACU8505-008.jpg
image:ACU8505-014.jpg
image:ACU8505-016.jpg
</gallery>
 [[Category:Peripherals]] [[Category:DIY]]