Commodore Amiga A500 Technical Reference Manual page 15

Time of Day Clock
Light Pen
In the A500, the Time of Day clock is tied to the VSYNC signal rather
than the power line. This results in the theoretical error of several
minutes a day. For more precise timing, use the optional real-time
clock.
In genlock mode, the genlock peripheral provides a
30
Hz VIZ signal,
which results in the clock running half speed.
The light pen input on the
A500
and B2000 has been moved to the
second mouse port to allow use without a pass-thru mouse adapter.
On a
B2000,
the light pen can be jumpered t o port 0 .
Monochrome
The
A500
and B2000 provide a full-bandwidth 16-level qrev-scale
Composite Video
composite video output. Color composite is available within bptional
A520 composite colorlrf video adapter.
Audio Filter C~t-out
The A500 and B2000 can cut out the anti-aliasing filter by program-
matically turning off the "power on" LED. External bandwidth limit-
ing to below 1 5
KHz
will be required for most applications. This per-
mits wider frequency response by using faster sampling rates.
AS00
Reset
The A500 implements a "hard-wired" Control/Commodore/Amiga
key reset rather than the " s o f t A1 000lA2000 keyboard reset.
"Shut down" keyboard messages are not transmitted.
A2000
Expansion Bus
The A2000 does not run the processor IPL lines beyond the 86 pin
IPL Lines
MMU
connector. Instead, additional interrupt request lines are allo-
cated for future expansion devices. These lines are not supported by
the current software.