w65c22 Western Design Center, Inc., w65c22 Datasheet - Page 30

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

The eight bidirectional lines D0-D7 are used to transfer data between the W65C22 and the microprocessor.
During a Read operation, the contents of the selected W65C22 internal register are transferred to the
microprocessor via D0-D7. During a Write operation, D0-D7 serve as high impedance inputs over which
data is transferred from the microprocessor to a selected W65C22 register.
impedance state when the W65C22 is unselected. The W65C22S has a bus holding device, in case the bus
tries to float, the data bus will be held in its previous state.
The IRQB output signal is logic 0 whenever an internal Interrupt Flag bit is set to logic 1 and the
corresponding Interrupt Enable bit is logic 1. The IRQB output is a full output driver that outputs both logic 1
and logic 0 levels. The W65C22N and older NMOS and CMOS IRQB output is/was an open drain pull
down only, thus allowing the IRQB signal to be wire ORed with an external resistor for a common
microprocessor IRQB input line. The W65C22S IRQB can be wire ORed with a pull down diode that is
forward biased when IRQB is low. See Figure 3.4 IRQB for the IRQB buffer schematics for both the
W65C22N and W65C22S.
The IRQB pin on the W65C22S is a standard totem pole output. The W65C22S IRQB signal was meant for
logically ORing rather than wire ORing the IRQ’s of a system. This change was made to improve the low
power, high speed characteristics of the part. For systems that have wire ORed IRQB outputs a solution is to
place a low voltage diode (<0.5V) in series with the W65C22S totem pole IRQB output.
3.4
3.5
Data Bus (D0-D7)
Interrupt Request (IRQB)
Figure 3-4 IRQB Buffer - W65C22N and W65C22S
D0-D7 are in the high
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