SI4706-D50 Datasheet, PDF (25/36 Pages) Silicon Laboratories – HIGH-PERFORMANCE FM AND RDS/RBDS RECEIVER

Si4706-D50
4.15. Control Interface
A serial port slave interface is provided, which allows an
external controller to send commands to the Si4706 and
receive responses from the device. The serial port can
operate in two bus modes: 2-wire mode and 3-wire
mode. The Si4706 selects the bus mode by sampling
the state of the GPO1 and GPO2 pins on the rising
edge of RST. The GPO1 pin includes an internal pull-up
resistor, which is connected while 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 11.
Table 11. Bus Mode Select on Rising Edge of
RST
Bus Mode
2-Wire
3-Wire
GPO1
1
0 (must drive)
GPO2
0
0
After the rising edge of RST, the pins GPO1 and GPO2
are used as general purpose output (O) pins as
described in Section “4.16. 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).
4.15.1. 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 Si4706 acknowledges the control word
by driving SDIO low on the next falling edge of SCLK.
Although the Si4706 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 Si4706 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 Si4706 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 Si4706.
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.
Rev. 1.0
25