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Application Note
AN_289 FT51A Programming Guide
Version 1.0
Document Reference No.: FT_000962 Clearance No.: FTDI# 483
60
Copyright © 2015 Future Technology Devices International Limited
2.8.1.1
DIGITAL_CONTROL_GPIO_0 to DIGITAL_CONTROL_GPIO_15
Bit
Position
Bit Field Name
Type
Reset
Description
7..6
RFU
R
0
Reserved
5
Sr
R/W
0
Slew Rate Control. When
sr
=0 slew
RATE is NORMAL. When
sr
=1 slew
RATE is SLOW
4
Smt
R/W
0
Schmitt Trigger Enable. When
smt
=1 the Schmitt circuit is
enabled, giving hysteresis on the
input signal. When
smt
=0 there is
no hysteresis.
3
pdena
R/W
0
Pull down Enable. When this signal
is set, a weak internal pull down is
enabled to hold the pad in a "low"
logic state if the pad is left
unconnected or tri-state
2
puena
R/W
0
Pull up Enable. When this signal is
set, a weak internal pull up is
enabled to hold the pad in a "high"
logic state if the pad is left
unconnected or tri-state
1..0
drive_strength
R/W
0
Drive strength control.
bit 1
bit 0
Drive
0
1
Weak
0
0
Low
1
0
Medium
1
1
High
Table 2.71 GPIO DIO Digital Control Registers
Note:
Do NOT set
puena
or
pdena
at the same time. This can place the port in an undetermined
state.
2.8.2
Analogue GPIO Pads
Up to 16 analogue I/O pads are available depending on package type. The analogue pads are
multi-speed, multi-voltage and bidirectional I/O. Each pad can function in either analogue or digital
mode, but not both modes at the same time.
For digital mode of operation each of the 16 AIO pads has its own control register shown in Table
2.72. The AIO_MODE register described in Section 2.10.3 is used to switch from analogue mode to
digital mode.