topic Re: Cheap, simple, and BDM in 8-bit Microcontrollers

Cheap, simple, and BDM

mke_et — Wed, 31 Jan 2007 23:02:05 GMT

Ok, I have a small 'favor' project I have to do for a Scout Troop. I figured I'd do it with an O8. My selection criteria of what I'm looking for includes:

BDM support
DIP package
Cheap

I want BDM support, since I have a USB-BDM cable, and at least some of the 08 family parts support BDM. That will make it a no-brainer to get it up and running quickly.

I want it in a DIP package, since I'm making only one of them for now, and will be attacking this with a wirewrap tool.

I want it Cheap, since this is a donation type thing, so I'm looking for what I can get as a free sample for a 1-up.

Ok, now that the important things are out of the way... I'll be using 1 serial com port, 8 inputs, and 8 outputs. If I have to, I can easily 'latch' the outputs on the same port as the inputs, and use an input buffer that is enabled and an output latch signal. I might also need two other inputs as switch inputs... But that may be later.

Any recomendations as to which 08 part to use?

I'd use a 9S12 part, since I have a badge or two floating around somewhere, but I don't want to give that up and loose the badge!

Mike

Re: Cheap, simple, and BDM

joerg — Thu, 01 Feb 2007 00:21:24 GMT

Hi Mike

If you can accept on a total of 14 pins + 2 for power) to use 2 pins for the serial communication TX/RX and having left 12 GPIO's; i would suggest the HCS08QG4/8 MPU.
(DIL case, with BDM)

Saluti Joerg

Re: Cheap, simple, and BDM

OldMan — Thu, 01 Feb 2007 03:04:15 GMT

I agree with joerg. QG4/8 seem to fit the bill. If you want one notch up, GT8A/16A are good too. 42 pin DIP, still below $2.

Re: Cheap, simple, and BDM

bigmac — Fri, 02 Feb 2007 01:06:39 GMT

Hello Mike,

If you want to stick with the 16-pin QG8 part, it may be satisfactory to get the additional I/O you need by using a couple of HCMOS shift registers in conjunction with the SPI module of the MCU, provided you don't need instantaneous control. I have previously used 74HC589 or 74HC597 device for parallel inputs, and 74HC595 for parallel outputs. Multiple devices can be cascaded if you need even more inputs or outputs - the amount of I/O by this method is independent of the number of pins on the MCU.

Regards,

Mac

Re: Cheap, simple, and BDM

mke_et — Fri, 02 Feb 2007 03:00:26 GMT

Thanks for the suggestion Bigmac, however, the 'input function' for the 8 bits I'm looking at is to find a 'first of many' and I need to be in a TIGHT loop to find it. I figure a 74HC240 as an input...

What I'm doing is looking at 8 inputs, and when the first one is hit, turn on a coresponding output to acknowledge it. Then on a hot-reset, start looking again, but mask off the prior hit. Then hot-reset yet again and so on, each time building up the mask until all the inputs are triggered. Then I do a master reset to start from scratch.

I figure 8 inputs/outputs, 2 switches for the resets, 2 control lines (1 to read a buffered input, the other to write a latched output, both from the 8-wide I/O bus), and serial I/O to report status as well as accept reset commands.

Mike

Re: Cheap, simple, and BDM

bigmac — Sat, 03 Feb 2007 06:27:43 GMT

Hello Mike,

A difficulty with using the QG8 part in the manner you describe - it has six pins available for PTA and eight pins for PTB, however, the SCI module occupies PTB0 and PTB1. This means that your eight signal lines will need to be shared between the two I/O ports. You will probably also need to forego the use of one of the signals, perhaps one of the resets, during the debug process, via BDM (PTA4).

Regards,

Mac