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C509-L_97 Datasheet, PDF (85/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller | |||
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On-Chip Peripheral Components
C509-L
The described activating and deactivating of the four different transistors results in four states which
can be:
â input low state (IL), p2 active only
â input high state (IH) = steady output high state (SOH), p2 and p3 active
â forced output high state (FOH), p1, p2 and p3 active
â output low state (OL), n1 active
If a pin is used as input and a low level is applied, it will be in IL state, if a high level is applied, it will
switch to IH state. If the latch is loaded with â0â, the pin will be in OL state. If the latch holds a â0â
and is loaded with â1â, the pin will enter FOH state for two cycles and then switch to SOH state. If
the latch holds a â1â and is reloaded with a â1â no state change will occur.
At the beginning of power-on reset the pins will be in IL state (latch is set to â1â, voltage level on pin
is below of the trip point of p3). Depending on the voltage level and load applied to the pin, it will
remain in this state or will switch to IH (=SOH) state.
If it is used as output, the weak pull-up p2 will pull the voltage level at the pin above p3âs trip point
after some time and p3 will turn on and provide a strong â1â. Note, however, that if the load exceeds
the drive capability of p2 (IIL), the pin might remain in the IL state and provide a week â1â until the
first 0-to-1 transition on the latch occurs. Until this the output level might stay below the trip point of
the external circuitry.
The same is true if a pin is used as bidirectional line and the external circuitry is switched from
output to input when the pin is held at â0â and the load then exceeds the p2 drive capabilities.
If the load exceeds IIL the pin can be forced to â1â by writing a â0â followed by a â1â to the port pin.
Semiconductor Group
6-7
1997-10-01
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