Can I disable LCD module by disconnecting Power to it -


i designing development board atmega328. want keep lcd module optional (hitachi hd44780, 2x16) . means solder lcd module on board, may not use if want use port pins other purpose. thinking of providing 1 jumper link vcc line of lcd (instead of providing several jumpers data , other signals) can remove jumper link , use port pins other purpose if lcd not needed. can this? port pins loaded if remove power lcd module or lcd module gets isolated? looked @ datasheet, not see internal connectivity of pins. may question applies many other devices well. disabling power device, can isolate device?

most lcd module have chip select or slave select pin (cs). if pin asserted (usually pulling low) module listen or send out data on data/address lines , sensitive clock.

other modules connect controller can have cs well.

by connecting cs pin gpio can select component want talk to, allowing connect multiple components same parallel data/address bus , multiplex communications. how it's done (and used happen long time talk plug in cards, isa , old parallel pci in pcs before there pci-express).

note displays may come 2 kinds of cs, 1 write , 1 read access. if both lines left unasserted (usually high), peripheral neutral. pulling both lines asserted invalid. pulling (write enable) make sensitive data writes xor pulling oe (output enable) make output data on pins.

update:

that means solder lcd module on board, may not use if want use port pins other purpose. thinking of providing 1 jumper link vcc line of lcd (instead of providing several jumpers data , other signals) can remove jumper link , use port pins other purpose if lcd not needed. can this?

most not! reason is, digital circuitry contains protective clamping diodes short circuit voltages outside operative range either gnd or vcc. there 2 kind of vcc range protection: rectifier vcc or zener gnd. in case of rectifier vcc voltage on signal lines greater 0.2 above peripheral's supply gets clamped. unpowered device either means, device parasitically draws current signal, powering circuitry (bad) or signals clamped gnd+0.2v (not either).

if lcd doesn't provide cs pins (unlikely) can insert bidirectional logic buffer (e.g. 74fct162245t) direction pin act cs circuit.


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