4 bit bus

[Bruce]

PortA = PortA & %00001111 would only work if the lower 4-bits were already set,
and would guarantee the higher 4-bits would be 0.

You want to OR the port with %00001111 to leave the higher 4-bits unaffected.

PortA = PortA | %00001111 would set the lower 4-bits, leaving the higher 4-bits
as-is.

[Art]

PortA = PortA & %00001111 would only work if the lower 4-bits were already set,
and would guarantee the higher 4-bits would be 0.

You want to OR the port with %00001111 to leave the higher 4-bits unaffected.

PortA = PortA | %00001111 would set the lower 4-bits, leaving the higher 4-bits
as-is.

Seems to be working thanks

Saves two words on setting the four bits one at a time.