I have an accelerator card fitted to my Amiga 1200. The accelerator includes a real-time clock, but I noticed that the soldered-on rechargeable battery was in danger of leaking, so I cut it off before it could leak and cause any damage. This leaves me without a fully working RTC; the accelerator card will presumably have an operational RTC chip that will forget the correct time as soon as powered off.

Can I connect an RTC card to the main board clockport? Would this work, or would its RTC chip clash with accelerator's RTC chip?

The accelerator is an Apollo 68060 card. It does not appear to have an enable/disable RTC switch or jumper. I would consider replacing the battery, but don't want to have another soldered-on rechargeable type, and the limited space on the card and in the trapdoor slot would make a coin cell conversion tricky.

Most likely, the two RTC devices would conflict, since they will probably rely on the same chip select line and base address $D80000.

Technically, the A1200 clock port and the A1200 expansion "trap-door" slot can support 2 separate clock port devices, since there are two chip selects. These are called the "RTC" CS, which uses $D80000-$D8FFFF, and the "SPARE" CS, which uses $DC0000-$DCFFFF. So, if you could assign each RTC chip to the two different CS lines, then they would respond on different addresses and would not conflict. However, this will require some minor hardware modification.

I see two likely options:

  1. (Good) Find an internal clock port RTC device that has a jumper to determine which CS/address it works off of. Naturally, the software driver will need to support the alternate address ($DC0000) too.
  2. (Bad) Disconnect the /RTCCS line from the accelerator card at the expansion port. This would require cutting a trace or a pin. Then a regular internal clock port RTC would use this CS line exclusively. No conflict.
  • 4
    Option 3, solder a new battery to the otherwise fully functioning accelerator card. – pipe Apr 25 '17 at 9:23
  • Make sure the disabled /CS is vcc-strapped or pullup-ed! – rackandboneman Aug 26 '17 at 16:15

Expanding on the comment made by @pipe:

Most if not all batteries originally used on the various Amigas and contemporary peripherals are rechargable NiCd (Nickel Cadmium) cells which are prone to leak.

If the battery is a common type, there is likely a drop-in replacement NiMH (Nickel Metal Hydride) battery which is rechargable and far less likely to leak, while allowing you to retain use of your existing RTC.

One can also replace the battery with a holder which will accept a Li-ion (Lithium Ion) battery akin to the ones used by mainstream PCs which are even less likely to leak. However, special care must be taken to prevent the motherboard from trying to charge the battery as it isn't rechargable. Usually this means cutting a circuit trace and adding a Germanium diode to the circuit.

Obviously these options require the use of a soldering iron.

I had a leaky battery on my Apollo 1240 card (it is the same PCB as the 1260) and desoldered it and replaced it with a Panasonic VL1220-1HFE rechargeable coin battery. Now the original battery had three pins, and the panasonic has two but I think the positive and negative terminals are marked on the card so just make sure you solder onto the right holes. The battery is larger than the original and extends past the sides of the card and the pins needed some creative "bending" to avoid the IC next to the battery. Otherwise no complaints - it has been working for two solid years.

I think this is the best solution. There is no need to a add second RTC and at any rate the Panasonic battery is more modern, rechargeable, and less likely to leak than the original and probably better than used RTC cards from eBay.

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