ESI Operation
974
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Extended Scan Interface (ESI)
Table 37-4. DAC Register Select When TESTDX=1
ESITESTS1(tsm)
DAC Register Used
0
ESIDAC1R6
1
ESIDAC1R7
37.2.1.7 Optional Comparator Offset Cancellation
The ESI's comparator has an offset that drifts over temperature and supply voltage. For some applications
the specified offset error and offset drift may be acceptable - see device-specific data sheet. If the offset
error is not acceptable, adding a comparator autozero cycle within the TSM sequence can minimize the
offset error. After the inserted autozero TSM cycle, the comparator operates effectively with a zeroed
offset.
Adding an ESITSMx state within the TSM sequence, which has the ESICAAZ bit selected
(ESITSM.ESICLKAZSEL=1) and set, performs the comparator autozeroing. As long as the ESICAAZ bit is
set the autozeroing is performed. This means, the length of the appropriate ESITSMx state defines the
length of autozeroing. The following code excerpt shows how to include an autozeroing cycle within a
TSM sequence. The example focus on ESICA and ESICAAZ control bits:
...
ESITSM5 = TSM_State5;
// TSM_State5 is a placeholder for any setting;
//
Comparator is
disabled (ESICA=0, ESICAAZ=0)
ESITSM6 = ESICA + E TSM_State6;
// comparator is switched on and at the same time the autozeroing is
// performed. Length is defined by ESCLK and ESIREPEATx bits -
// appropriate setting needed to meet autozeroing timing requirements;
// see device-specific data sheet (ESICA=1, ESICAAZ=1)
ESITSM7 = ESICA + TSM_State7;
// normal comparator operation: settle comparator
// (ESICA=1, ESICAAZ=0)
ESITSM8 = ESICA + TSM_State8;
// normal comparator operation: processing of comparator output signal
// (ESICA=1, ESICAAZ=0)
...
37.2.2 ESI Timing State Machine
The TSM is a sequential state machine that cycles through the ESITSMx registers and controls the analog
front end and sensor excitation automatically with no CPU intervention. The states are defined within a 32
x 16-bit memory, ESITSM0 to ESITSM31. The ESIEN bit enables the TSM. The ESI uses ACLK as its
source for the low frequency clock signal ESILFCLK. When ESIEN = 0, the ACLK input divider, the TSM
start flip-flop, and the TSM outputs are reset and the internal oscillator is stopped. The TSM block diagram
is shown in
.
A TSM sequence begins at ESITSM0 and ends when the TSM encounters a ESITSMx state with a set
ESITSTOP bit. When a state with a set ESISTOP bit is reached, the state counter is reset to zero and
state processing stops. State processing re-starts at ESITSM0 with a software trigger (setting the
ESISTART control bit), the next start condition when ESITSMRP = 0, or immediately when ESITSMRP = 1
After generation of the ESISTOP(tsm) pulse, the timing state machine will load and maintain the
conditions defined in ESITSM0. For the case an LC sensor is used the ESILCEN(tsm) bit should be reset
in ESITSM0 to ensure that all LC oscillators are shorted (damped) while no measurement sequence is in
progress.
In case a TSM sequence is started with a software trigger, the ESISTART control bit is automatically
cleared as soon as a TSM sequence is completed and the system is again in idle mode (ESITSM0
settings are used in idle mode).