GX3146 Datasheet, PDF (38/46 Pages) Semtech Corporation – Crosspoint Switch with Trace Equalization and Output De-emphasis

4.12.2 Serial Host Interface Specifications
The Gennum Serial Peripheral Interface (GSPI) handles the communication with an
external host over the SPI port. It allows configuration of the Control and Status
Registers (CSR) using serial read and write operations.
The GX3146 GSPI is selected by setting the HOST_S/P pin HIGH.
Note 1: The P_CS pin must be pulled LOW when HOST_S/P is set HIGH for serial port
communication.
The GX3146 uses a four-wire protocol, with serial communication via the input SDIN
pin, the output SDOUT pin, clock input signal (SCLK), and the chip select signal (S_CS).
The signalling rate can be up to 25Mb/s. The interface uses 16-bit data and a 16-bit
address/control. The 16-bit address and control consists of a 12-bit address, one
read/write bit (‘1’ for read, ‘0’ for write), one bit for auto-increment and two unused bits.
The four-wire protocol is implemented as shown in Figure 4-11 and Figure 4-12.
When the Auto-Increment bit is set LOW, each Command Word must be followed by
only one Data Word to ensure proper operation.
If the Auto-Increment bit is set HIGH, the following Data Word is written into the
address specified in the Command Word, and subsequent Data Words are written into
incremental addresses from the first Data Word. This facilitates multiple address reads
or writes without sending a Command Word for each Data Word.
Table 4-17: GSPI Inputs/Outputs
Signal Name
SCLK
SDIN
SDOUT
S_CS
I/O
Reference
Clock
Description
I
—
GSPI clock
I
SCLK
GSPI serial data input
O
SCLK
GSPI serial data output (on the negative edge of
SCLK)
I
—
GSPI Chip Select
t0
t1
t2
t4
SCLK
S_CS
SDIN
SDOUT
t3
t8
R
RSV
RSV Auto_Inc A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
R/W
RSV
RSV Auto_Inc A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
t7
D15 D14 D13 D12 D11 D10 D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
D15 D14 D13 D12 D11 D10 D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
SDIN signal is looped out on SDOUT
Figure 4-11: Serial Host Interface Timing Diagram - Write Mode
GX3146 146 x 146 3.5Gb/s Crosspoint
Final Data Sheet Rev. 2
GENDOC-056075 March 2013
www.semtech.com
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