ST92F124/F150/F250 - GENERAL DESCRIPTION
1.4 I/O PORTS
Port 0, Port 1 and Port 9[7:2] provide the external
memory interface. All the ports of the device can
be programmed as Input/Output or in Input mode,
compatible with TTL or CMOS levels (except
where Schmitt Trigger is present). Each bit can be
programmed individually (Refer to the I/O ports
chapter).
ble 3), while the High Hysteresis Schmitt Trigger is
present on ports P4[7:6] and P6[5:4].
All inputs which can be used for detecting interrupt
events have been configured with a “Standard”
Schmitt Trigger, apart from the NMI pin which im-
plements the “High Hysteresis” version. In this
way, all interrupt lines are guaranteed as “edge
sensitive”.
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.
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
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”.
V
+0.3 Volt, to avoid direct junction biasing.
DD
Pure Open-Drain Output
The user can increase the voltage on an I/O pin
Schmitt Trigger Input
over V +0.3 Volt where the P-channel MOS tran-
DD
sistor is physically absent: this is allowed on all
“Pure Open Drain” pins. In this case, the push-pull
option is not available and any weak pull-up must
be implemented externally.
Two different kinds of Schmitt Trigger circuitries
are implemented: Standard and High Hysteresis.
Standard Schmitt Trigger is widely used (see Ta-
Table 3. I/O Port Characteristics
Input
Output
Push-Pull/OD
Push-Pull/OD
Weak Pull-Up
No
No
Reset State
Bidirectional
Bidirectional
Port 0[7:0]
Port 1[7:0]
TTL/CMOS
TTL/CMOS
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
Push-Pull/OD
Yes
No
Yes
Yes
Input
Input CMOS
Input
Input CMOS
1)
Port 3[2:0]
Port 3.3
Port 3[7:4]
Schmitt trigger
TTL/CMOS
Schmitt trigger
Push-Pull/OD
Push-Pull/OD
Push-Pull/OD
Yes
Yes
Yes
Input
Input CMOS
Input
Port 4.0, Port 4.4
Port 4.1
Port 4.2, Port 4.5
Port 4.3
Schmitt trigger
Schmitt trigger
TTL/CMOS
Schmitt trigger
High hysteresis Schmitt trigger Pure OD
Push-Pull/OD
Push-Pull/OD
Push-Pull/OD
Push-Pull/OD
No
Input
Yes
Yes
Yes
No
Bidirectional WPU
Input CMOS
Input
Port 4[7:6]
Input
Port 5[2:0], Port 5[7:4] Schmitt trigger
Push-Pull/OD
Push-Pull/OD
No
Yes
Input
Input CMOS
Port 5.3
TTL/CMOS
Port 6[3:0]
Port 6[5:4]
Port 6[7:6]
Schmitt trigger
High hysteresis Schmitt trigger Push-Pull/OD
Schmitt trigger
Push-Pull/OD
Yes
Yes
Yes
Input
Input
Input
1)
Push-Pull/OD
Port 7[7:0]
Schmitt trigger
Push-Pull/OD
Yes
Input
Port 8[1:0]
Port 8[7:2]
Schmitt trigger
Schmitt trigger
Push-Pull/OD
Push-Pull/OD
Yes
Yes
Input
Bidirectional WPU
Port 9[7:0]
Schmitt trigger
Push-Pull/OD
Yes
Bidirectional WPU
Legend:
WPU = Weak Pull-Up, OD = Open Drain.
Note 1: Port 3.0 and Port6 [7:6] present on ST92F250 version only.
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