Functional Modes
11
SLLU250 – November 2016
Copyright © 2016, Texas Instruments Incorporated
BOOSTXL-RS232 BoosterPack™ Hardware
4
Functional Modes
The BOOSTXL-RS232 BoosterPack has three modes of operation: On with Auto-Powerdown Plus
enabled, Forced On, and Forced Off. Included in this section is the discussion of the INVALID pin.
4.1
Auto-Powerdown Plus
Auto-Powerdown Plus is enabled when FORCEON is set LOW and FORCEOFF is set HIGH. Using the
integrated edge-detection circuitry and timer of the TRS3122E, the device can sense when there is no
activity on the driver or receiver inputs for 30 seconds. When this condition is sensed by the device, it
automatically shuts the charge pump off, reducing supply current to 0.5 µA. When a valid transition is
sensed on one of the driver or receiver inputs, the charge pump turns back on and TRS3122E exits
powerdown mode. The typical time to exit powerdown mode is typically 30 µs, but can be as long as 150
µs. As a result, the system saves power without requiring any software control. While in the low power
mode with Automatic Powerdown enabled (FORCEOFF = HIGH and FORCEON = LOW), the receiver
inputs are still enabled.
The FORCEON and FORCEOFF pins control the power states of the transceiver. When the jumpers short
FORCEON to GP19 and FORCEOFF to GP18, the power down states of the transceiver can be controlled
through GPIO, see
and
4.2
Forced On
If the FORCEON and FORCEOFF pins are both set HIGH, the device will power on with Auto-Powerdown
Plus disabled. Both the drivers and receivers will be active regardless of inactivity, as shown in
and
4.3
Forced Off
The device can be manually powered down by externally setting the FORCEOFF pin LOW. Both the
drivers and receivers will be powered off, as shown in
and
. This mode overrides the other
modes.
(1)
H = high level, L = low level, X = irrelevant, Z = high impedance (off), 30 s is typical inactivity time
Table 2. Driver Functions
(1)
Inputs
Output
Driver Status
DIN
FORCEON
FORCEOFF
Time Elapsed Since Last
RIN or DIN Transition
DOUT
X
X
L
X
Z
Powered off
L
H
H
X
H
Normal operation with
auto-powerdown plus disabled
H
H
H
X
L
L
L
H
< 30 s
H
Normal operation with
auto-powerdown plus enabled
H
L
H
< 30 s
L
L
L
H
> 30 s
Z
Powered off by
auto-powerdown plus feature
H
L
H
> 30 s
Z
(1)
H = high level, L = low level, X = irrelevant, Z = high impedance (off), Open = input disconnected or connected driver off
Table 3. Receiver Functions
(1)
Inputs
Output
Receiver Status
RIN
FORCEOFF
Time Elapsed Since Last
RIN or DIN Transition
ROUT
X
L
X
Z
Powered off
L
H
X
H
Normal operation with
auto-powerdown plus
disabled or enabled
H
H
X
L
Open
H
X
H
