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ST92F120 - GENERAL INFORMATION
1.3 I/O PORTS
Port 0 and Port 1 provide the external memory in-
terface. All the ports of the device can be pro-
grammed as Input/Output or in Input mode, com-
patible with TTL or CMOS levels (except where
Schmitt Trigger is present). Each bit can be pro-
grammed individually (Refer to the I/O ports chap-
ter).
Internal Weak Pull-up
As shown in
Table 3, not all input sections imple-
ment a Weak Pull-up. This means that the pull-up
must be connected externally when the pin is not
used or programmed as bidirectional.
TTL/CMOS Input
For all those port bits where no input schmitt trig-
ger is implemented, it is always possible to pro-
gram the input level as TTL or CMOS compatible
by programming the relevant PxC2.n control bit.
Refer I/O Ports Chapter to the section titled “Input/
Output Bit Configuration”.
Schmitt Trigger Input
Two different kind of Schmitt Trigger circuitries are
implemented: Standard and High Hysteresis.
Standard Schmitt Trigger is widely used (see
Ta-ble 3), while the High Hysteresis one is present on
the NMI and VPWI input function pins mapped on
All inputs which can be used for detecting interrupt
events have been configured with a “standard”
Schmitt Trigger, apart from, as already said, the
NMI pin which implements the “High Hysteresis”
version. In this way, all interrupt lines are guaran-
teed as “l(fā)evel sensitive”.
Push-Pull/OD Output
The output buffer can be programmed as push-
pull or open-drain: attention must be paid to the
fact that the open-drain option corresponds only to
a disabling of P-channel MOS transistor of the
buffer itself: it is still present and physically con-
nected to the pin. Consequently it is not possible to
increase the output voltage on the pin over
VDD+0.3 Volt, to avoid direct junction biasing.
Pure Open-drain Output
The user can increase the voltage on an I/O pin
over VDD+0.3 Volt where the P-channel MOS tran-
sistor is physically absent: this is allowed on all
“Pure Open Drain” pins. Of course, in this case the
push-pull option is not available and any weak
pull-up must implemented externally.
Table 3. I/O Port Characteristics
Legend: WPU = Weak Pull-Up, OD = Open Drain
Input
Output
Weak Pull-Up
Reset State
Port 0[7:0]
TTL/CMOS
Push-Pull/OD
No
Bidirectional
Port 1[7:0]
TTL/CMOS
Push-Pull/OD
No
Bidirectional
Port 2[1:0]
Port 2[3:2]
Port 2[5:4]
Port 2[7:6]
Schmitt trigger
TTL/CMOS
Schmitt trigger
TTL/CMOS
Push-Pull/OD
Pure OD
Push-Pull/OD
Yes
No
Yes
Input
Input CMOS
Input
Input CMOS
Port 3[2:1]
Port 3.3
Port 3[7:4]
Schmitt trigger
TTL/CMOS
Schmitt trigger
Push-Pull/OD
Yes
Input
Input CMOS
Input
Port 4.0, Port 4.4
Port 4.1
Port 4.2, Port 4.5
Port 4.3
Port 4[7:6]
Schmitt trigger
TTL/CMOS
Schmitt trigger
Schmitt trigger inside I/O cell
Push-Pull/OD
Pure OD
No
Yes
No
Input
Bidirectional WPU
Input CMOS
Input
Port 5[2:0], Port [7:4]
Port 5.3
Schmitt trigger
TTL/CMOS
Push-Pull/OD
No
Yes
Input
Input CMOS
Port 6[3:0]
Port 6[5:4]
Schmitt trigger
High hysteresis Schmitt trigger
inside I/O cell
Push-Pull/OD
Yes
Yes (inside I/O cell)
Input
Port 7[7:0]
Schmitt trigger
Push-Pull/OD
Yes
Input
Port 8[1:0]
Port 8[7:2]
Schmitt trigger
Push-Pull/OD
Yes
Input
Bidirectional WPU
Port 9[7:0]
Schmitt trigger
Push-Pull/OD
Yes
Bidirectional WPU
9