gc80c520a CORERIVER Semiconductor, gc80c520a Datasheet - Page 30

• Manufacturer Part Number: gc80c520a
• Description: Midas1.0 Family Mask Rom/eprom/romless 8-bit Turbo Microcontrollers
• Manufacturer: CORERIVER Semiconductor

For another practical example, P3.2 is used as the /INT0 input pin. If external interrupt 0 is enabled, a
logic 0 input to P3.2 will generate external interrupt 0. Then by disabling the external interrupt 0, P3.2 will
return to a general purpose I/O pin. So the interrupt is used to “wake-up” the system from power saving
modes.
6.2.1.5 PORT 4
Port 4 is an 4-bit bi-directional I/O port with internal pull-up resistors. The pull-up resistors are switched
on/off by the value of the SFR P4SEL. Port 4 pins that have 1s written to them are pulled high weakly by
the internal pull-up resistors and can be used as inputs. Its output pins are push-pull drived.
CPU BUS
CPU BUS
Alternative Function Output
P4.0
SFR
P3.0
Figure 6-8 Configuration of PORT3
Figure 6-9 Configuration of PORT4
Digital Input
SFR
Digital Input
QB
Q
QB
Q
2 OSC
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Pulse
2 OSC
Pulse
Functional Description
Pull-
up
Pull-
up
P3SEL.0
P4SEL.0