SC658ULTRT Semtech, SC658ULTRT Datasheet - Page 15

• Manufacturer Part Number: SC658ULTRT
• Description: Backlight Driver For 4 LEDs With SemPulseTM Interface
• Manufacturer: Semtech

SemPulse
SemPulse Timing Diagrams
The SemPulse single wire interface is used to enable or disable the device and configure all registers (see Figure 3). The
timing parameters refer to the digital I/O electrical specifications.
Timing Example 1
In this example (see Figure 4), the slave chip receives two sets of pulses to set the address and data, and the pulses expe-
rience interrupts that cause the pulse width to be nonuniform. Note that as long as the maximum high and low times
are satisfied and the hold times are within specification, the data transfer is completed regardless of the number of
interrupts that delay the transmission.
Timing Example 2
In this example (see Figure 5), the slave chip receives two sets of pulses to set the address and data, but an interrupt
occurs during a pulse that causes it to exceed the minimum address hold time. The write is meant to be the value 03h
in register 05h, but instead it is interpreted as the value 02h written to register 02h. The extended pulse that is delayed
by the interrupt triggers a false address detection, causing the next pulse set to be interpreted as the data set. To avoid
any problems with timing, make sure that all pulse widths comply with their timing requirements as outlined in this
datasheet.
TM
SPIF
SPIF
Interface (continued)
SPIF
Figure 5 — Faulty SemPulse Data Write Due to Extended Interrupt Duration
t = t
Figure 3 — Uniform Timing Diagram for SemPulse Communication
Figure 4 — SemPulse Data Write with Non-Uniform Pulse Widths
t = t
SU
SU
Up to 32 rising edges
Address is set to
register 02h
(0 to 31 pulses)
t
HI
Interrupt
duration
t > t
HImax
t < t
HImax
Address is set
Address is set to
register 02h
t = t
HOLDA
Data written is
t = t
000010
HOLDA
t = t
Up to 64 rising edges
HOLDA
t
(0 to 63 pulses)
HI
t < t
t
LO
LOmax
03h (address and data are
Address is set to register
now out of order)
t = t
t
LO
HOLDD
Data written is
t = t
Data is written
000011
HOLDD
t = t
HOLDD
SC658
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