8-bit MicrocontrollersのトピックRe: 908JK3 programmer - unused MCU pins floating or not?

908JK3 programmer - unused MCU pins floating or not?

JimDandy — Sun, 02 Aug 2009 17:58:25 GMT

Just putting together a simple programmer board for a '908JK3. The schematic in the

data book doesn't show what to do with the MCU pins that are not used for programming.

Should they be left floating or grounded? I strongly suspect grounded but things are not

always obvious.

Re: 908JK3 programmer - unused MCU pins floating or not?

mnemonic — Mon, 10 Aug 2009 04:35:03 GMT

Hello!

A little late...

Fabio Pereira wrote in Chapter 13 in his book "HCS08 Unleashed"

Unused Pins must be configured as outputs (and left open) or configured as inputs and tied to Vdd or Vss. Unconnected input pins can draw current in excess and pick up noise. The advantage of configuring the pin to output mode and leaving it unconnected is the possibility of future usage (which is not so simple when the pin is connected to Vdd or Vss).

A really good Book!

best regards

Ingo Kauf

Re: 908JK3 programmer - unused MCU pins floating or not?

JimDandy — Mon, 10 Aug 2009 16:10:34 GMT

Hi mnemonic.

I understand what you mean when the mcu is used in the actual application, but when being programmed the data manual on page 103 in the monitor rom section shows several pins

being tied high or low via a 10k resistor and the others are either part of the programming situation

or simply not drawn on the diagram. It is these last pins I am wondering about.

In the 'HC908QY4A manual on pages 146-147 it shows programming examples where the pins

are simply left floating.

Re: 908JK3 programmer - unused MCU pins floating or not?

mnemonic — Mon, 10 Aug 2009 22:27:11 GMT

Hello Jim!

I´ve never tryed to connect unused pins from an mcu to a potential (Vdd or Vss) in programming mode. If I am not sure in such a case, I try to find a schematic from a Demoboard which using this mcu. I always let these pins open. I never got trouble.

Try to find the Freescale App Note AN2317. May there is some interresting information for you.

I tryed the schematic on page 13, in works fine!

good Luck

Ingo Kauf