The second PIA has a smaller mirror in the CoCo 3 than the CoCo 1/2. It goes from $FF20 to $FF2F. The CoCo 1/2 mirror is from $FF20 to $FF3F.

Recently I was challenged to find a citation for this information. But I could not. Tepolt has this wrong. So I decided to create a test program and accompanying video to document this first hand.

Here is the test program.

It is a menu driven program that allows you to choose a specific mirror address for PIA 2, then allows you to choose one of three tests.

Test ‘S’ produces a square wave using the CoCo’s DAC. This DAC is connect to port A of the PIA.
Test ‘B’ produces a square wave using the CoCo 1 bit sound source. This is connected to bit 1 of port B of the PIA.
Test ‘V’ toggles the A/G line of the VDG. This is connected to bit 7 of port B of the PIA.

When using this program on a CoCo 3 you will find the the second PIA only responds from $FF20 to $FF2F. And the VDG test only responds to $FF20 to $FF23, because the GIME only see writes to these specific addresses.