Pad Control and Pinmux
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47
PUPDC = 0 and PD = 1
Off
Off
Off
On
10k pull-down
PUPDC = 1 and PD = 1
Off
On
Off
Off
4.7k pull-down
PUPDC =
x
and PU = 1 and PD = 1
The setting is not allowed
6.2.3
Pad Schmitt Trigger
All I/O pins include a schmitt trigger that can be selectively disabled by setting the PAD_BIT_SCHMITT_TRIGGER_EN bit in the PADCTRL register.
The specification of schmitt trigger is listed in Table 6-3.
Table 6-3 Schmitt trigger specification
I/O Power
1.8V
3.3V
Schmitt trigger
VIH: (0.65*VDD) V
VIL: (0.35*VDD) V
VIH: 2V
VIL: 0.8V
6.2.4
Pad Driving Strength
The I/O pad driving strength can be configured through PAD_BIT_DRIVING_STRENGTH field in the PADCTRL register, as shown in Table 6-4. Pad
driving strength is different between different pad types.
Table 6-4 Normal pad driving strength configuration
Pad Driving Strength
1.8V
3.3V
0
2mA
4mA
1
4mA
8mA
2
6mA
12mA
3
8mA
16mA
6.2.5
Pad Shut Down
The power of a I/O pad can be shut down through the PAD_BIT_SHUT_DWON bit in the PADCTRL register. You can use this function to
conserve power.
6.2.6
I
2
C Open-drain Mode
Pins that support I
2
C with specialized pad electronics have additional configuration bits. These bits have multiple configurations to support I
2
C
variants. They are not hard-wired so that the pins can be more easily used for non-I
2
C function.
In Fig 6-1, signal “E” and signal “I” are used to select push-pull mode or open-drain mode, the two signals are controlled by hardware
automatically. For example, when you select I
2
C function for this pin, open-drain mode is selected.
Post Driver Output Mode
E
I
IO
Normal GPIO
1
Driven by GPIO module
Push-pull output
I
2
C
Driven by I
2
C module
0
Open-drain output
Pay attention that PB[5] and PB[6] can also be set to I
2
C function, but their pull resistors only support 50kohm. So 4.7kohm external pull-up
resistors should be added to ensure I
2
C work properly.
6.2.7
Audio Pad
These pins − PA[0] ~ PA[6], PB[28] ~ PB[31] are sharing with audio function. Take care when using these pins as other function except audio.
When audio function is used, the audio LDO voltage is set to 2.8V. The AVCC of this pad can only reach to 2.8V.
When audio function is not used, it is necessary to set AVCC to 3V above and use these pins as normal GPIO, as Table 6-5 shows.
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2019-05-15 10:08:03