Re: 6522 VIA inputs

Date: Fri, 21 Apr 2017 12:11:42 +0200
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> On 2017-04-21, at 11:47, Pasi 'A1bert' Ojala <> wrote:
> CMOS uses push-pull drives, but my impression is that older technologies use pull-ups with open-collector/open-drain drives. I.e. passive up, active down.
> CMOS can emulate open-drain drive by using an external pull-up resistor and switching between input (high-impedance) and drive-0 states. I have used this often to create I2C using regular IO pins.
> Microcontrollers often have weak pull-downs or pull-ups. However, resistors in the MOhm range increase the production testing time due to the requirement to measure very small currents, which is a reason they are not always used. (In addition to having a minimal effect in leakage during low-power modes.)

Pasi, thanks - that's the very reason I am looking closer at it! I want to output data to VIA port pins acting as inputs and started to wonder whether I should drive the lines HI (seems to work in tests but if the lines are in fact pulled up then it's presumably unneeded/undesirable) or rather tri-state my outputs instead.

SD! -

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