topic Re: MC908QB8 board design questions in 8-bit Microcontrollers

MC908QB8 board design questions

Andre_PT — Wed, 11 Jul 2007 01:07:53 GMT

Hi all,

I'm new with the HC08 and its MON08 programming interface. Normally I work with the HC12 (BDM).

Thing is that I need to design a new board with the MC908QB8 (16 pin) and looking at the MON08 interface, it seams that 6 pins of the MCU will be used for the MON08 interface... I need to use those pins for the application so my questions are:

1) What is the best way to program/debug the MC908GB8 without loosing the MON08 6 pins of the MCU?

2) Is it possible to continuing to use all the MCU pins for application purposes instead of MON08 interface without using additional signal switching hardware?

It's a pity that the MC9S08QG8 is low voltage...

Thanks in advance for your comments,

Andre

Re: MC908QB8 board design questions

bigmac — Wed, 11 Jul 2007 11:50:30 GMT

Hello Andre,

There are two separate issues here - in-circuit programming and debug. The programming will be more staight forward.

For in-circuit programming, the six pins, PTA0 to PTA5 associated with MON08 should present a sufficiently high impedance (say 10k) to the programming device, or should be capable of being isolated, perhaps by means of jumper or switch, from external circuitry that presents a low impedance.

An additional consideration applies to PTA2 - whatever is connected to that pin must also be able to withstand the higher programming voltage applied to the pin by the programmer. Also the programmer will apply a high frequency clock to PTA5, so the external capacitance at this pin must be low, or isolated with a series resistance.

Note that, if the external circuitry causes the power-up state of PTA1 and PTA3 to be high, and PTA4 to be low, these connections need not be extended to the MON08 connection.

Personally, I do not like using the standard 16-way header arrangement for MON08 - it would seem to make the MCU more susceptible to damage by static discharge, etc because of the exposed header pins.

Debug presents a different situation since control over four of the pins must be maintained by the MON08 device, and are therefore not available to the application during debug. For serious debug capability, you would need to use an ICE.

Interestingly, AN2305 describes a "user mode monitor" for QT and QY devices that permits debug using a single dedicated pin (no high voltage and no external oscillator required). However, this concept has not been extended to the QB device.

Regards,

Mac

Re: MC908QB8 board design questions

UcTechnoGeek — Thu, 12 Jul 2007 00:31:04 GMT

If you can spend the extra $0.50, I'd go with the 9S08AW16.

It's uses the S08 core, so more than likely, your HCS12 tools will work on it as well.

The 9S08AW family works at the higher 5.0V.

uCTechnoGeek

Re: MC908QB8 board design questions

Andre_PT — Thu, 12 Jul 2007 16:48:44 GMT

UcTechnoGeek (and all),

First of all thanks for your comments.

The problem is not only about the price, it is more about the package type and pin count. I'm looking for a small DIP uC (say DIP16) that has SCI, SPI, does not need external crystal and has some I/O pins (price should be less than $2.00)...

In these conditions the best solutions I came up with are the MC908QB8 and the MC9S08QG8. If the MC9S08QG8 was a 5V uC I would chose it with no second thoughts but putting the uC at 3.3V and the rest of the electronics at 5V is a little risky and I would need to use open-collector buffers in all output pins for voltage level conversion... (Don't know if there is a better way to do it though...).

I also need to store a few bytes in non-volatile memory so the feature of using the internal Flash for non-volatile user data storage is very handy. This way I will not need a serial EEPROM to store a few bytes.

My main problem is obviously lack of knowledge on how to correctly use the MON08 and spare the I/O pins as much as possible.

In other threads I found some information regarding a small software routine to erase the vector address and perform a mass erase triggered by a logic value in on of the I/O pins after the POR (Pull-Down in /IRQ). I think this is a good idea for pin saving since the forced monitor mode entry will than be possible (Only the PTA0 will be necessary). The thing is that for debug purposes the pins really need to be tied to MON08 (say for example with the Cyclone Pro and Metrowerks to make step-by-step debug?)

I will be waiting for your comments and suggestions.

Best regards to all,

Andre

Re: MC908QB8 board design questions

bigmac — Thu, 12 Jul 2007 17:33:44 GMT

Hello Andre,

What peripherals does your application really require? If you do not need the SCI facility, you may be able to alternatively use the QY4A device. You could then implement the code to allow user mode monitor access, to obtain the simpler debug arrangement. This would then require only the PTA0 connection to be continuously available during debug operation.

The user monitor requires a small amount of code to be interleaved at the highest flash page, and would be programmed there, along with your application code, using the Multilink or Cyclone Pro device in a conventional manner. The full MON08 arrangement would still be required for programming.

Regards,

Mac

Message Edited by bigmac on 2007-07-12 08:36 PM