[Coco] Re: [Color Computer] Re: Interfacing question.

[Gene Heskett]

On Tuesday 22 March 2005 14:40, j_e_daggett wrote:
>Phil
>
>What pin of the 22V10 is the A3 line driving? Pin #1 is either an
>input or a clock input. It is advisable that pin #1 be the E clock
>line. Logic should be set so that teh address is decoded on the
> rising edge of the E clock. Make sure that the macrocell associated
> for A3 is also programmed for combinatorial mode and not registered
> mode.
>
>Word of caution on the MC6809E. The address bus output driver
>trtansistors are NMOS depletion load. That is the output transistor
> is a NMOS depletion transistor with another NMOS depletion
> transistor with the gate connected in diode fashion and this takes
> the place of the load resistor in the drain circuit. When driving a
> TTL compatible input to logic High, the 6809 can only source
> (current flowing out) about 400 microamps max. Driving the TTL
> input to a low the 6809 can sink (current flowing in) of 2 ma max.
>
>The problem is the Coco has so much already on the address buss
>internally that they had to add internal pullups to maintain the
> logic levels with the output high signals. By adding a pullup
> externally suggests that the PLD is requireing to much current when
> a login one is presented or the A3 line, the internal pullup
> resistor is not soldered properly or the A3 pin of the MPU is not
> to spec.
>
>In the case of PLD requireing too much current for the MPU on logic
>high, you may have to add buffers to the address buss lines.
>
>
>james
>
Or switch to a 6309, which can cheerfully source or sink 20 ma per 
pin, and its logic one outputs are the supply rail for all practical 
purposes.

[...]

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
99.34% setiathome rank, not too shabby for a WV hillbilly
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2005 by Maurice Eugene Heskett, all rights reserved.


Brought to you by the 6809, the 6803 and their cousins! 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/ColorComputer/

<*> To unsubscribe from this group, send an email to:
    ColorComputer-unsubscribe at yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/