Si4734/35-C40
Rev. 1.0 25
RST is low, and the GPO2 pin includes an internal pull-
down resistor, which is connected while RST
is low.
Therefore, it is only necessary for the user to actively
drive pins which differ from these states. See Table 13.
After the rising edge of RST
, the pins GPO1 and GPO2
are used as general purpose output (O) pins, as
described in Section “5.17. GPO Outputs”. In any bus
mode, commands may only be sent after V
IO
and V
DD
supplies are applied.
In any bus mode, before sending a command or reading
a response, the user must first read the status byte to
ensure that the device is ready (CTS bit is high).
5.16.1. 2-Wire Control Interface Mode
When selecting 2-wire mode, the user must ensure that
SCLK is high during the rising edge of RST
, and stays
high until after the first start condition. Also, a start
condition must not occur within 300 ns before the rising
edge of RST
.
The 2-wire bus mode uses only the SCLK and SDIO
pins for signaling. A transaction begins with the START
condition, which occurs when SDIO falls while SCLK is
high. Next, the user drives an 8-bit control word serially
on SDIO, which is captured by the device on rising
edges of SCLK. The control word consists of a 7-bit
device address, followed by a read/write bit (read = 1,
write = 0). The Si4734/35 acknowledges the control
word by driving SDIO low on the next falling edge of
SCLK.
Although the Si4734/35 will respond to only a single
device address, this address can be changed with the
SEN
pin (note that the SEN pin is not used for signaling
in 2-wire mode). When SEN
= 0, the 7-bit device
address is 0010001b. When SEN
= 1, the address is
1100011b.
For write operations, the user then sends an 8-bit data
byte on SDIO, which is captured by the device on rising
edges of SCLK. The Si4734/35 acknowledges each
data byte by driving SDIO low for one cycle, on the next
falling edge of SCLK. The user may write up to 8 data
bytes in a single 2-wire transaction. The first byte is a
command, and the next seven bytes are arguments.
For read operations, after the Si4734/35 has
acknowledged the control byte, it will drive an 8-bit data
byte on SDIO, changing the state of SDIO on the falling
edge of SCLK. The user acknowledges each data byte
by driving SDIO low for one cycle, on the next falling
edge of SCLK. If a data byte is not acknowledged, the
transaction will end. The user may read up to 16 data
bytes in a single 2-wire transaction. These bytes contain
the response data from the Si4734/35.
A 2-wire transaction ends with the STOP condition,
which occurs when SDIO rises while SCLK is high.
For details on timing specifications and diagrams, refer
to Table 5, “2-Wire Control Interface Characteristics” on
page 7; Figure 2, “2-Wire Control Interface Read and
Write Timing Parameters,” on page 8, and Figure 3, “2-
Wire Control Interface Read and Write Timing Diagram,”
on page 8.
5.16.2. 3-Wire Control Interface Mode
When selecting 3-wire mode, the user must ensure that
a rising edge of SCLK does not occur within 300 ns
before the rising edge of RST
.
The 3-wire bus mode uses the SCLK, SDIO, and SEN
_
pins. A transaction begins when the user drives SEN
low. Next, the user drives a 9-bit control word on SDIO,
which is captured by the device on rising edges of
SCLK. The control word consists of a 9-bit device
address (A7:A5 = 101b), a read/write bit (read = 1, write
= 0), and a 5-bit register address (A4:A0).
For write operations, the control word is followed by a
16-bit data word, which is captured by the device on
rising edges of SCLK.
For read operations, the control word is followed by a
delay of one-half SCLK cycle for bus turn-around. Next,
the Si4734/35 will drive the 16-bit read data word
serially on SDIO, changing the state of SDIO on each
rising edge of SCLK.
A transaction ends when the user sets SEN
high, then
pulses SCLK high and low one final time. SCLK may
either stop or continue to toggle while SEN
is high.
In 3-wire mode, commands are sent by first writing each
argument to register(s) 0xA1–0xA3, then writing the
command word to register 0xA0. A response is
retrieved by reading registers 0xA8–0xAF.
For details on timing specifications and diagrams, refer
to Table 6, “3-Wire Control Interface Characteristics,” on
page 9; Figure 4, “3-Wire Control Interface Write Timing
Parameters,” on page 9, and Figure 5, “3-Wire Control
Interface Read Timing Parameters,” on page 9.
Table 13. Bus Mode Select on Rising Edge of
RST
Bus Mode GPO1 GPO2
2-Wire 1 0
SPI 1 1 (must drive)
3-Wire 0 (must drive) 0
