Cypress PSoC 4000 Series - Page 49

PSoC 4000 Family: PSoC 4 Architecture TRM, Document No. 001-89309 Rev. *D 49
I/O System
Figure 7-3. I/O Drive Mode Block Diagram
■ High-Impedance Analog
High-impedance analog mode is the default reset state; both output driver and digital input buffer are turned off. This state
prevents an external voltage from causing a current to flow into the digital input buffer. This drive mode is recommended for
pins that are floating or that support an analog voltage. High-impedance analog pins cannot be used for digital inputs. Read-
ing the pin state register returns a 0x00 regardless of the data register value. To achieve the lowest device current in low-
power modes, unused GPIOs must be configured to the high-impedance analog mode.
■ High-Impedance Digital
High-impedance digital mode is the standard high-impedance (High Z) state recommended for digital inputs. In this state, the
input buffer is enabled for digital input signals.
■ Resistive Pull-Up or Resistive Pull-Down
Resistive modes provide a series resistance in one of the data states and strong drive in the other. Pins can be used for either
digital input or digital output in these modes. If resistive pull-up is required, a ‘1’ must be written to that pin’s Data Register bit.
If resistive pull-down is required, a ‘0’ must be written to that pin’s Data Register. Interfacing mechanical switches is a com-
mon application of these drive modes. The resistive modes are also used to interface PSoC with open drain drive lines.
Resistive pull-up is used when input is open drain low and resistive pull-down is used when input is open drain high.
■ Open Drain Drives High and Open Drain Drives Low
Open drain modes provide high impedance in one of the data states and strong drive in the other. The pins can be used as
digital input or output in these modes. Therefore, these modes are widely used in bi-directional digital communication. Open
drain drive high mode is used when signal is externally pulled down and open drain drive low is used when signal is externally
pulled high. A common application for open drain drives low mode is driving I
2
C bus signal lines.
■ Strong Drive
The strong drive mode is the standard digital output mode for pins; it provides a strong CMOS output drive in both high and
low states. Strong drive mode pins must not be used as inputs under normal circumstances. This mode is often used for digi-
tal output signals or to drive external transistors.
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
DR
PS
Pin
0. High Impedance
Analog
1. High Impedance
Digital
2. Resistive Pull Up 3. Resistive Pull Down
4. Open Drain,
Drives Low
5. Open Drain,
Drives High
6. Strong Drive
7. Resistive Pull Up
and Pull Down
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