HP-25C Eumulator

[Chris Chung]

(11-25-2014 03:55 PM)Harald Wrote:  

(11-20-2014 04:10 PM)Chris Chung Wrote:  Actually if I use a Atmel mega328/168 (28 pins), the circuit will be cleaner and reduce to just 1 IC (no shift register needed). But I haven't use AVRs for quite awhile now and it's more interesting to do it w/ an MSP430.

Why not use the MSP430G2533IPW28? That has 28 pins as well. I thought about doing that, but to be honest so far I didn't even find the time to look at the datasheet...

Edit:
I just had another look, the demoboard comes with an MSP430G2553. Your code also says 2553, but in your post you mention 2533. I haven't got your board handy to check, but I guess its the 2553. Anyhow, the differences appear to be minute and the 2553 is available as a 28 pin device too.

I started w/ 2553 (adc + comparator) since it comes w/ the launchpad and I had lots of it. When I order for kits I get the 2533 (adc only) as it's more available and less expensive. The project only requires a 2513 (no adc nor comparator).

The 2553 has all the peripherals but in our case, we only need IO pins for led multiplexing and key scanning.

As for the 28 pin devices, they are only available on TSSOP packages. If we use one of these, it will be a one chip design as we will have enough IO pins to drive everything. I.e. no 74LS164 and the tricky one-line shifting. It just happened that I am more inclined to use DIP devices as it's easier to build for everyone. /EDIT Also I think DIP device looks better in a retro project /END-EDIT. Now that I look again, a TSSOP is not too bad to hand solder except that it is not commonly carried by my usual supplier (newark.com) and could be harder to get.

If I am to do it again, I would move to a F2274 (38 pin tssop) and I will be able to to fit another HP-34C inside w/ doubled flash and RAM.

There are many improvement possibilities, like instead of shut-off, we could make the MCU deep sleep at LPM4 (low-power-mode 4) and have RAM retention (continuous memory), the MSP430 at this mode consumes only 0.1uA.