Operation of the USS Module
454
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Ultrasonic Sensing Solution (USS, USS_A)
18.2.1 Auto Mode and Register Mode
The USS or USS_A module can perform the full data acquisition sequence with minimum involvement of
CPU, which enables ultra-low power consumption during the measurement and frees the CPU from data
acquisition, so that the ultrasonic application software can be executed in parallel to data acquisition with
minimum intervention. The USS or USS_A module also support register mode, in which each
measurement sequence is controlled by user software. Register mode can be used during development
and for special tasks like diagnostics.
To enable the auto mode, apply the configurations in
before turning on the USS or USS_A
module.
Table 18-1. Auto Mode and Register Mode
Auto Mode Configuration
Action
Register Mode
UUPSCTL.SWRST = 0
Take USS submodules out of reset (once after reset)
UUPSCTL.SWRST = 0
SAPHMCNF.LPBE = 0
Enable auto mode or register mode (on mode
changes)
SAPHMCNF.LPBE = 0
UUPSCTL.LBHDEL = 0, 1, 2, or 3
Set optimal start-up hold-off delay or leave at default
UUPSCTL.LBHDEL = 0, 1, 2, or 3
SAPHMCNF.BIMP = 0, 1, 2, or 3
Set optimal bias impedance or leave at default
SAPHMCNF.BIMP = 0, 1, 2, or 3
UUPSCTL.ASQEN = 1
PSQ to trigger ASQ when power is up
(PSQ_START) (on mode changes)
UUPSCTL.ASQEN = 0
SAPHASCTL0.TRIGSEL = 1
ASQ is triggered by PSQ (on mode changes)
SAPHASCTL0.TRIGSEL = 0
SAPHOSEL.PCH0SEL = 1
SAPHOSEL.PCH1SEL = 1
Drive output drivers to GND (on mode changes)
SAPHOSEL.PCH0SEL = 0
SAPHOSEL.PCH1SEL = 0
SAPHBCTL.ASQBSW = 1
Tx bias, Rx bias control (on mode changes)
SAPHBCTL.ASQBSW = 0
SAPHPGCTL.PGSEL = 1
Select output channel in PPG (on mode changes)
SAPHPGCTL.PGSEL = 0
SAPHPGCTL.TRSEL = 1
Trigger PPG (on mode changes)
SAPHPGCTL.TRSEL = 0
SAPHICTL0.MUXCTL = 1
Input channel selection (on mode changes)
SAPHICTL0.MUXCTL = 0
SDHSCTL0.TRGSRC = 1
SDHS power up and conversion trigger source (on
mode changes)
SDHSCTL0.TRGSRC = 0
SDHSCTL0.AUTOSSDIS = 1
SDHS conversion trigger (on mode changes)
SDHSCTL0.AUTOSSDIS = 0 or 1
SDHSCTL2.SMPCTLOFF = 0
(optional)
Total sample size is preprogrammed (on mode
changes)
SDHSCTL2.SMPCTLOFF = 0 or 1
SDHSCTL2.DTCOFF = 0
Data transfer by DTC (on mode changes)
SDHSCTL2.DTCOFF = 0 or 1
18.2.1.1 Six Time Mark Events in Auto Mode
In auto mode, the six time mark registers generate important timing events during measurement.
describes the time mark events.
Table 18-2. Time Mark Events
Time Mark
Action by ASQ
PSQ_START= 0
→
1
Apply Tx Bias
ASQ time counter = Value in SAPHATM_A register
Trigger PPG to generate excitation pulses and stop pulses
ASQ time counter = Value in SAPHATM_B register
Turn on the SDHS
ASQ time counter = Value in SAPHATM_C register
Apply Rx Bias
ASQ time counter = Value in SAPHATM_D register
Start sampling the input signal (trigger the SDHS)
ASQ time counter = Value in SAPHATM_E register
Restart the time counter for the next measurement
ASQ time counter = Value in SAPHATM_F register
Time-out
18.2.1.2 How to Start in Auto Mode
In auto mode, the entire measurement sequence is executed by the PSQ and the ASQ. The start-up
sequence is simple but the following order must be used: