Physical Interface (PHY) Block
505
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Sequencer for Acquisition, Programmable Pulse Generator, and Physical
Interface (SAPH, SAPH_A)
When SAPHOSEL.PCH0SEL = 2, the two output pins working as differential output drivers. The pulses
generated by PPG are output on both pins differentially.
When SAPHOSEL.PCH0SEL = 1 or 2, the two pins are controlled by the PPG block and ASQ block. The
pins are automatically enabled when PPG generates pulses. The SWG0 and SWG1 switches are
controlled by ASQ as part of measurement sequence (see
The drive strength of DRV0 and DRV1 are maximized when SAPHOCTL1.CH0FP = 1 and
SAPHOCTL1.CH1FP = 1, respectively. The drive strength of the pins are determined by SAPHCH0PUT,
SAPHCH0PDT, SAPHCH1PUT, and SAPHCH1PDT when SAPHOCTL1.CH0FP = 0 and
SAPHOCTL1.CH1FP = 0, respectively (see
When SAPHOSEL.PCH0SEL = 1 or 2, the two pins are controlled by the PPG block and ASQ block. The
pins are automatically enabled when PPG generates pulses. The SWG0 and SWG1 switches are
controlled by ASQ as part of measurement sequence (see
21.3.2 Trim Registers for the Output Drivers and Termination Resistors
The output channels (CH0_OUT and CH1_OUT) have low-impedance output drivers (DRV0 and DRV1)
and termination switches (SWG0 and SWG1). To support the impedance-matching requirement in
application environments using ultrasonic technology, programmability is offered to the output drive
strength of the drivers (DRV0 and DRV1) and the termination switches (SWG0 and SWG1). The drivers
are based on inverter architecture, which consists of PMOS and NMOS. Thus, three trim registers are
offered for each channel (see
for details).
During manufacturing, optimal impedance of the drivers and termination switches are determined and their
trim values are stored to the device boot data memory (not user accessible). The output impedance of
DRV0 and DRV1 are trimmed to match each other (with the lowest possible value), and the termination
switches (SWG0 and SWG1) are trimmed to match the impedance of each driver. During the boot
process, the trim values are written to the trim registers by bootcode. The default trim values may be
different from device to device. Programmability is offered if different impedance values are preferred in a
specific application environment.
(1)
See the device-specific data sheet for details.
Table 21-1. Trim Registers
Register
Description
Trim Range (Typical)
(1)
SAPHCH0PUT.CH0PUT
PMOS trim bits (4 bits) for the channel 0 output driver
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
SAPHCH0PDT.CH0PDT
NMOS trim bits (4 bits) for the channel 0 output driver
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
SAPHCH0TT
Termination switch trim bits (4 bits) for channel 0
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
SAPHCH1PUT.CH1PUT
PMOS trim bits (4 bits) for the channel 1 output driver
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
SAPHCH1PDT.CH1PDT
NMOS trim bits (4 bits) for the channel 1 output driver
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
SAPHCH1TT
Termination switch trim bits (4 bits) for channel 1
15 = lowest (
≈
2.5
Ω
)
0 = highest
Each step
≈
3%
The trim registers are written with the default values during every boot up; thus, if different trim values are
preferred, the values must be written to the trim registers by software after every boot.
NOTE:
To avoid unintended writes to the trim registers, the SAPHTACTL.UNLOCK bit can block
write access to the trim registers. The trim registers are locked when
SAPHTACTL.UNLOCK = 0.