By adding some resistors it's possible to control four displays on each 16F628.
This is true if the circuit driving this display unit are capable of both sourcing and sinking the signal (i.e. not open collector) and can handle an extra load of 100 uA.
The same pins on the '628 can be connected both to the displays via 220 ohm resistors as well as the outputs from the controlling circuit via 47 Kohm resistors.
The '628 will first set the pins as input, read the incoming signal, calculate the correct bitpattern, set the ports as outputs, output the bitpattern, wait 20 mS and repeat all over again.
This means that the segments on the display can only be changed 50 times per second, but i think that's enough...
The attached picture only shows half of the circuit. It needs to be repeated for portB.
Mike: What program are you using to draw your schematics?
EDIT - I just realized that it's not possible to drive four displays this way using the 628 since the RA5 -port is crippled and can only be used as an input. This input/output sharing thing can be used in other applications to reduce the number of ports required, but for this specific application it's not usable. Sorry.
This is true if the circuit driving this display unit are capable of both sourcing and sinking the signal (i.e. not open collector) and can handle an extra load of 100 uA.
The same pins on the '628 can be connected both to the displays via 220 ohm resistors as well as the outputs from the controlling circuit via 47 Kohm resistors.
The '628 will first set the pins as input, read the incoming signal, calculate the correct bitpattern, set the ports as outputs, output the bitpattern, wait 20 mS and repeat all over again.
This means that the segments on the display can only be changed 50 times per second, but i think that's enough...
The attached picture only shows half of the circuit. It needs to be repeated for portB.
Mike: What program are you using to draw your schematics?
EDIT - I just realized that it's not possible to drive four displays this way using the 628 since the RA5 -port is crippled and can only be used as an input. This input/output sharing thing can be used in other applications to reduce the number of ports required, but for this specific application it's not usable. Sorry.
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