gc80c520a CORERIVER Semiconductor, gc80c520a Datasheet - Page 27

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

MiDAS1.0 Family
port 0 latch during any access to external memory. The internal pull-up resistors are switched on/off by
the value of P0SEL. Only P0.0 can be used as an analog input of an A/D converter. It is assigned as
analog inputs via the bit 0 of the register ADCSEL.
When used for accessing external memory, Port 0 provides the data byte time-multiplexed with the low
byte of the address. In this state, Port 0 is disconnected from its own port latch, and the address/data
signal drives push-pull FETs in its output buffer. In this application, Port 0 uses strong internal pull-ups
when emitting 1s. During any access to external memory, the CPU writes FFH to the port 0 latch, thus
obliterating whatever information the port SFR may have been holding. When maximizing the slew rate,
special protection circuits prevent ringing, excessive noise, and interface problems. No external pull-up
resistor is needed since it degrades the memory access timing.
External Address/Data
P0SEL.0
Pull-
External Access
up
Q
CPU BUS
P0.0
SFR
QB
Digital Input
ADC Block Input
ADC0
Figure 6-5 Configuration of PORT 0
Note: During external access, P0 SFR will automatically set to “FFh”.
Note: Read-Modify-Write instructions do not read port pin but SFR register.
6.2.1.2 PORT 1
Port 1 is an 8-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 P1SEL. Port 1 pins that have 1s written to them are pulled high weakly by
the internal pull-up resistors and can be used as inputs. Port 1 pins can be also used alternate functions.
To use the alternate functions, the corresponding bit of the Port 1 pin should be set to high. The alternate
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