Cirrus Logic CS5378 - Manual (Page 64)

CS5378
DS639F3 64
19. GENERAL PURPOSE I/O
The General Purpose I/O (GPIO) block provides 8
general purpose pins to interface with external
hardware.
19.1 Pin Descriptions
GPIO[3:0] - Pins 4 - 1
Standard GPIO pins.
GPIO[6:4]:PLL[2:0] - Pins 7 - 5
Standard GPIO pins also used to select the PLL
mode after reset. Internal pull-ups default high,
10 k
Ω external pull-downs required to set low.
GPIO7:BOOT - Pin 28
Standard GPIO pin also used to select boot mode
after reset. Internal pull-up defaults high, 10 k
Ω ex-
ternal pull-down required to set low.
19.2 GPIO Architecture
Each GPIO pin can be configured as input or out-
put, high or low, with a weak (~100 k
Ω) internal
pull-up resistor enabled or disabled. Figure 38
shows the structure of a bi-directional GPIO pin.
19.3 GPIO Registers
GPIO pin settings are programmed in the GPCFG
register. GP_DIR bits set the input/output mode,
GP_PULL bits enable/disable the internal pull-up
resistor, and GP_DATA bits set the output data val-
ue. After reset, GPIO pins default as inputs with
pull-up resistors enabled.
19.4 GPIO Input Mode
When reading a value from the GP_DATA bits, the
returned data reports the current state of the pins. If
a pin is externally driven high it reads a logical 1, if
externally driven low it reads a logical 0. When a
GPIO pin is used as an input, the pull-up resistor
should be disabled to save power if it isn’t required.
19.5 GPIO Output Mode
When a GPIO pin is programmed as an output with
a data value of 0, the pin is driven low and the in-
ternal pull-up resistor is automatically disabled.
When programmed as an output with a data value
of 1, the pin is driven high and the pull-up resistor
is inconsequential.
Any GPIO pin can be used as an open-drain output
by setting the data value to 0, enabling the pull-up,
and using the GP_DIR direction bits to control the
pin value. This open-drain output configuration
uses the internal pull-up resistor to hold the pin
high when GP_DIR is set as an input, and drives the
pin low when GP_DIR is set as an output.
Figure 38. GPIO Block Diagram
GPIO
GP_DIR
GP_DATA
GP_PULL Pull Up
Logic
R