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AN-004: W65C22S Replacement Notes for Obsolete VIA Devices


The W65C22S can replace older and obsolete NMOS and CMOS versions of the 6522 Versatile Interface Adapter (VIA) supplied by WDC′s licensees. The W65C22S is manufactured on TSMC′s latest .6u process node with full RoHS and Green compliant manufacturing processes. Our chips are all fully static and therefore work from 0Hz to 8MHz and beyond; so your old 1, 2, 3, and 4MHz parts are easily replaced with in some cases minor board changes.








Comparison of 6522, W65C22S, R65C22 and G65SC22

1. On older versions of the 6522 and 65C22, which are not internally chip-selected, random register are read due to register select values. The W65C22S selects only register 15 ($F) internally. This feature has been added for systems which have indeterminate register select values.

2. 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.

3. There is a major design difference between the W65C22S and all previous versions of the 6522 and 65C22. The IRQB pin on the W65C22S is a standard totem pole output. It is no longer open drain and cannot be wire OR'ed. This change was made to improve the low power, high speed characteristics of the part.

4. WDC removed the internal pull-up resistors that were present on the NMOS R6522 and active pull-up transistors on the GTE G65SC22 and added bus holding devices on the W65C22S. The W65C22S design reduces power and speeds up the transition to a for applications that don't require pull-up resistors. Also, it should be noted that when driving Darlington transistors a current limiting resistor may be required for the W65C22S. The NMOS R6522 had built-in limiting with the pull-up resistor on PA port and smaller P channel transistors on the PB port. The GTE G65SC22 had active transistor pull-up devices on both the PA and PB ports that provided pull-up current when in the input mode. All W65C22S pins except PHI2 have bus holding devices. The original NMOS 6522, G65C22 and R65C22 did not have bus holding devices.




G65SC22PEI vs. W65C22SPL
G65SC22PEI W65C22SPL
VSS VSS
PA0 PA0
PA1 PA1
PA2 PA2
PA3 PA3
PA4 PA4
PA5 PA5
PA6 PA6
PA7 PA7
PB0 PB0
NC NC
PB1 PB1
PB2 PB2
PB3 PB3
PB4 PB4
PB5 PB5
PB6 PB6
PB7 PB7
CB1 CB1
CB2 CB2
VDD VDD
NC NC
IRQB IRQB
RWB RWB
CS2B CS2B
CS1 CS1
PHI2 PHI2
D7 D7
D6 D6
D5 D5
D4 D4
D3 D3
NC NC
D2 D2
D1 D1
D0 D0
RESB RESB
NC NC
RS3 RS3
RS2 RS2
RS1 RS1
RS0 RS0
CA2 CA2
CA1 CA1


Comments

1. IRQB on current versions of the W65C22SPL can drive high or low. IRQB on older versions of the W65C22 can only drive low.
2. The W65C22SPL has bus holding devices on all pins except PHI2.
3. The G65SC22PEI does not have bus holding devices.
  

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