13-12-2021, 06:47 PM
If a system already has a functioning MC1481818 fitted, the best solution would be to replace the old NiCad with a Ni-MH, small 3.6V pak's are prolific for use in solar garden lights.
I would steer clear of button cells for this chip as it is a lot more power hungry than the latter DS12887 which has internal clock circuitry and internal Lithium battery.
If you need to replace the MC1481818 with a DS12887A or add clock function to a Premium Microbee that has none, then there are a couple of things you need to watch out for. It has been quite a few years since I did one but as best I can tell from my notes.
1) The DS12887A is configurable for either Motorola or Intel timing - we need it to be configured for Motorola this is done by holding pin 1 at Logic high. Pin 1 on the Premium it connected to the +5V rail, so we need to cut the track at IC18 (RTC) pin 1 on the top side between CV2 and the RTC. Connect a jumper from Pin 1 to Pin 24.
2) Remove all the Clock components from pins 2 & 3 - CV2, C7, R3, G1 &R4 absolutely necessary C8 may as well while at it. Also remove R14, C6 D1, D2, R7 & R1, Cut the track to Pin 20.
3) We now need to provide isolated +5V power tp Pin 24 of the RTC so the internal battery doesn't flatten over night while trying to run the Microbee. Use a Schottky diode from a convenient 5V to Pin 24, I fitted the anode end of mine in the cathode pad of D1 +5V and the cathode end in the cathode end of D2.
4 There is a vague reference to a jumper to restore +5V power to IC15 - maybe a track gets interrupted when we cut power to pin 22 of the RTC, not 100% sure there.
Ernest
I would steer clear of button cells for this chip as it is a lot more power hungry than the latter DS12887 which has internal clock circuitry and internal Lithium battery.
If you need to replace the MC1481818 with a DS12887A or add clock function to a Premium Microbee that has none, then there are a couple of things you need to watch out for. It has been quite a few years since I did one but as best I can tell from my notes.
1) The DS12887A is configurable for either Motorola or Intel timing - we need it to be configured for Motorola this is done by holding pin 1 at Logic high. Pin 1 on the Premium it connected to the +5V rail, so we need to cut the track at IC18 (RTC) pin 1 on the top side between CV2 and the RTC. Connect a jumper from Pin 1 to Pin 24.
2) Remove all the Clock components from pins 2 & 3 - CV2, C7, R3, G1 &R4 absolutely necessary C8 may as well while at it. Also remove R14, C6 D1, D2, R7 & R1, Cut the track to Pin 20.
3) We now need to provide isolated +5V power tp Pin 24 of the RTC so the internal battery doesn't flatten over night while trying to run the Microbee. Use a Schottky diode from a convenient 5V to Pin 24, I fitted the anode end of mine in the cathode pad of D1 +5V and the cathode end in the cathode end of D2.
4 There is a vague reference to a jumper to restore +5V power to IC15 - maybe a track gets interrupted when we cut power to pin 22 of the RTC, not 100% sure there.
Ernest