w65c134s Western Design Center, Inc., w65c134s Datasheet - Page 58

• Manufacturer Part Number: w65c134s
• Description: W65c134s 8-bit Microcontroller
• Manufacturer: Western Design Center, Inc.

Figure 5-9 W65C134S Resonator Circuit
5.4
Wait state information and uses for the BE pin
The BE pin has two functions;
allowing DMA into the W65C134S (BE function) and stopping the
microprocessor (RDY function). Changing BE during PHI2 low time changes the BE function; changing BE
during PHI2 high time changes RDY. If you want to stop the processor, you should pull BE low in the PHI2
high time for as many cycles as needed. Pulling the BE low in PHI2 high time does not tristate the memory
bus. Note also that the PHI2 pin does not stay high while RDY is pulled low; PHI2 going out will continue
normally regardless of BE.
Pulling BE low during PHI2 low time turns off the output buffers on the address pins; however, the pins do
not float because of weak bus holding devices. Note that the addresses are really inputs to the W65C134S
when BE is low. If an external driver puts an address on the bus while BE is low, internal memory (RAM,
ROM, or memory-mapped registers) will be accessed depending on the state of WEB. If you have no desire
to turn off the busses when you slow down for the peripheral chips, you should hold BE high while you hold
RDY low. That is,
BE = (PHI2BAR or RDY)
where PHI2BAR is PHI2 inverted and delayed at least 10ns.
RDY is your signal to request the
microprocessor to stop. If you are not using the FCLK oscillator, another (less desirable) way to stop the
microprocessor is to extend the low or high time of FCLK as long as you need to. This will work only if you
know the microprocessor is using FCLK, not CLK.
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