Texas Instruments Digital Signal Processor SM320F2812-HT User Manual
Page 79
Peripheral I/O
MUX
0
1
MUX
1
0
PIN
Internal (Pullup or Pulldown)
Digital I/O
XRS
High-Impedance
Enable (1)
High-
Impedance
Control
GPxDIR
Register Bit
GPxMUX
Register Bit
GPxQUAL
Register
GPxDAT/SET/CLEAR/TOGGLE
Register Bit(s)
Input Qualification
SYSCLKOUT
SGUS062B
–
JUNE 2009
–
REVISED JUNE 2011
shows how the various register bits select the various modes of operation for GPIO function.
A.
In the GPIO mode, when the GPIO pin is configured for output operation, reading the GPxDAT data register only
gives the value written, not the value at the pin. In the peripheral mode, the state of the pin can be read through the
GPxDAT register, provided the corresponding direction bit is zero (input mode).
B.
Some selected input signals are qualified by the SYSCLKOUT. The GPxQUAL register specifies the qualification
sampling period. The sampling window is 6 samples wide and the output is only changed when all samples are the
same (all 0
'
s or all 1
'
s). This feature removes unwanted spikes from the input signal.
Figure 4-12. GPIO/Peripheral Pin Multiplexing
NOTE
The input function of the GPIO pin and the input path to the peripheral are always enabled. It
is the output function of the GPIO pin that is multiplexed with the output path of the primary
(peripheral) function. Since the output buffer of a pin connects back to the input buffer, any
GPIO signal present at the pin is propagated to the peripheral module as well. Therefore,
when a pin is configured for GPIO operation, the corresponding peripheral functionality (and
interrupt-generating capability) must be disabled. Otherwise, interrupts may be inadvertently
triggered. This is especially critical when the PDPINTA and PDPINTB pins are used as GPIO
pins, since a value of zero for GPDDAT.0 or GPDDAT.5 (PDPINTx) puts PWM pins in a
high-impedance state. The CxTRIP and TxCTRIP pins also put the corresponding PWM pins
in high impedance, if they are driven low (as GPIO pins) and bit EXTCONx.0 = 1.
Copyright
©
2009
–
2011, Texas Instruments Incorporated
Peripherals
79
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