How to increase drive capabitity of DP256 IO ports

Started by linktek September 19, 2003
Hi,

I need to increase the drive capacity from the meager 2.5mA per IO pin to
about 20mA per IO pin for 8 IO lines. Now the
trick is to retain the bi-direction function of the IO pins. How can I
increase the the output drive of the DP256 IO pins without
loosing input capabitity with a solution that will fit on a dime?
Frank



The "Electrical Characteristics" of the DP256 manual say that the IO
pins already have max 25 mA current, so maybe you don't need to do
anything?! On Freitag, Sep 19, 2003, at 15:35 Europe/Paris, linktek wrote:

>
> Hi,
>
> I need to increase the drive capacity from the meager 2.5mA per IO pin
> to
> about 20mA per IO pin for 8 IO lines. Now the
> trick is to retain the bi-direction function of the IO pins. How can I
> increase the the output drive of the DP256 IO pins without
> loosing input capabitity with a solution that will fit on a dime? >
> Frank >
> ------------------------ Yahoo! Groups Sponsor
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>





Frank,

The recommended operating conditions of the DP256 allow sourcing or sinking
10mA per normal I/O pin, when the I/O is configured for full-drive.

In reduced drive, the I/O can sink or source 2mA.

(the absolute maximum rating specify 25mA - but it is not recommended to
operate the I/O in this current)

If you can use another HCS12 derivative, the 9S12H256 and H128 have 24 I/O
line (Ports U, V, and W) with increased I/O drive - allowing 20mA for both
sink and source currents.

An option to increase the drive and maintain the input capability involves
2 i/o pins per generated higher current pin:
You can use a 74ACT126 and a 74ACT125 (that allow 24mA source and sink
current) connected as follows:

A) The input of the 126 and the output of the 125 are connected to the
DP256 I/O pin which serves as the input/output I/O.

B) The output of the 126 and the input of the 125 are connected together to
form your higher current input/output signal.

C) A second I/O from the DP256 is connected to the control input of both
the 126 and 125, to control the data flow direction. Note the 126 and 125
have opposite active control (126 is active when control is high, and 125
is active when control is low). Thus when the DP256 control pin will be
high the direction for the generated high-current i/o is output, and when
the DP256 control pin will be low the direction for the generated
high-current i/o is input.

Hope this helps,
Doron
Nohau Corporation
HC12 In-Circuit Emulators
www.nohau.com/emul12pc.html

At 04:06 PM 9/19/2003 +0200, you wrote:
>The "Electrical Characteristics" of the DP256 manual say that the IO
>pins already have max 25 mA current, so maybe you don't need to do
>anything?!
>
>On Freitag, Sep 19, 2003, at 15:35 Europe/Paris, linktek wrote:
> > Hi,
> >
> > I need to increase the drive capacity from the meager 2.5mA per IO pin
> > to
> > about 20mA per IO pin for 8 IO lines. Now the
> > trick is to retain the bi-direction function of the IO pins. How can I
> > increase the the output drive of the DP256 IO pins without
> > loosing input capabitity with a solution that will fit on a dime?
> >
> >
> >
> > Frank