w65c22 Western Design Center, Inc., w65c22 Datasheet - Page 48

• Manufacturer Part Number: w65c22
• Description: W65c22n And W65c22s Versatile Interface Adapter Via Datasheet
• Manufacturer: Western Design Center, Inc.

5. CAVEATS
On older versions of the 6522 and 65C22, which are not internally chip selected, random register are read
due to register select values. The W65C22 selects only register 15 ($F) internally. This feature has been
added for systems which have indeterminate register select values.
When outputting the Shift Clock, the CB1 pin may be overdriven without affecting the shifting function.
However, this is not recommended as it will result in high currents and possible damage to the part.
Because some systems have been arbitrating the clock after data has been transferred, this feature was
added.
All W65C22S pins except PHI2 have bus holding devices. The original NMOS 6522, W65C22N,
G65SC22, and R65NC22 did not have bus holding devices.
The W65C22S output pins do not have current limiting and can over drive circuitry connected to these
pins. The original NMOS 6522 and W65C22N have current limiting resistors in series with PB and PA
outputs.
5.1
5.2
5.3
5.4
Older Versions
Shift Clock
Bus Holding Pins
Current Limiting
Figure 5-1 High Resistance Bus Holding Device on the W65C22S
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