W79E825A Datasheet, PDF (91/127 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E825A/824A/823B/822B Data Sheet
20 I/O PORT CONFIGURATION
The W79E825 series have three I/O ports, port 0, port 1 and port 2. All pins of I/O ports can be
configured to one of four types by software except P1.5 is only input pin. When P1.5 is configured
reset pin by RPD=0 in the CONFIG 1 register, the W79E825 series can support 15 pins by use
Crystal. If used on-chip RC oscillator the P1.5 is configured input pin, the W79E825 series can be
supported up to 18 pins. The I/O ports configuration setting as below table.
PXM1.Y
0
0
PXM2.Y
0
1
1
0
1
1
Table 20-1: I/O port Configuration Table
PORT INPUT/OUTPUT MODE
Quasi-bidirectional
Push-Pull
Input Only (High Impedance)
P2M1.PxS=0, TTL input
P2M1.PxS=1, Schmitt input
Open Drain
All port pins can be determined to high or low after reset by configure PRHI bit in the CONFIG1
register. After reset, these pins are in quasi-bidirectional mode. The port pin of P1.5 only is a Schmitt
trigger input.
Enabled toggle outputs from Timer 0 and Timer 1 by T0OE and T1OE on P2M1 register, the output
frequency of Timer 0 or Timer 1 is by Timer overflow.
Each I/O port of the W79E825 series may be selected to use TTL level inputs or Schmitt inputs by
P(n)S bit on P2M1 register, where n is 0, 1 or 2. When P(n)S is set to 1, Ports are selected Schmitt
trigger inputs on Port(n). The P2.0 (XTAL2) can be configured clock output when used on-chip RC or
external Oscillator is clock source, and the frequency of clock output is divided by 4 on on-chip RC
clock or external Oscillator.
20.1 Quasi-Bidirectional Output Configuration
After chip was power on or reset, the all ports output are this mode, and output is common with the
8051. This mode can be used as both an input and output without the need to reconfigure the port.
When the pin is pulled low, it is driven strongly and able to sink a fairly large current. These features
are somewhat similar to an open drain output except that there are three pull-up transistors in the
quasi-bidirectional output that serve different purposes.
This mode has three pull-up resisters that are “strong” pull-up, “weak” pull-up and “very weak” pull-up.
The “strong” pull-up is used fast transition from logic “0” change to logic “1”, and it is fast latch and
transition. When port pins is occur from logic “0” to logic “1”, the strong pull-up will quickly turn on two
CPU clocks to pull high then turn off.
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Publication Release Date: February 21, 2008
Revision A9