GS2972 Datasheet, PDF (87/125 Pages) Semtech Corporation – 3G/HD/SD-SDI Serializer with Complete SMPTE Audio & Video Support

4.13 GSPI Host Interface
Note: When using more than one Semtech serializer or deserializer (SerDes) in the same
design, carefully read this section to see how the GSPI ports of multiple ICs should be
connected to each other. Unlike some previous devices, the SDOUT pin of these SerDes
ICs is a non-clocked, loop-through of SDIN (allowing for multiple devices to be
connected to the GSPI chain). The SDOUT pins of multiple SerDes ICs should not be
bussed together, as was the case with some older generations of SerDes ICs.
The GSPI, or Gennum Serial Peripheral Interface, is a 4-wire interface provided to allow
the application layer to access additional status information through configuration
registers in the GS2972.
The GSPI comprises a Serial Data Input signal (SDIN), Serial Data Output signal (SDOUT),
an active-low Chip Select (CS) and a Burst Clock (SCLK).
Because these pins can be shared with the JTAG interface port for compatibility with the
GS1582, an additional control signal pin JTAG/HOST is provided.
When JTAG/HOST is LOW, the GSPI interface is enabled. When JTAG/HOST is HIGH, the
JTAG interface is enabled.
When operating in GSPI mode, the SCLK, SDIN, and CS signals are provided by the
application interface. The SDOUT pin is a non-clocked loop-through of SDIN, and may
be connected to the SDIN of another device, allowing multiple devices to be connected
to the GSPI chain. The interface is illustrated in Figure 4-29 below.
Application Host
SCLK
CS1
SDOUT
GS2972
SCLK
CS
SDIN
SDOUT
CS2
SDIN
GS2972
SCLK
CS
SDIN
SDOUT
Figure 4-29: GSPI Application Interface Connection
All read or write access to the GS2972 is initiated and terminated by the application host
processor. Each access always begins with a Command/Address Word followed by a
data read to or written from the GS2972.
GS2972 3G/HD/SD-SDI Serializer with Complete
SMPTE Audio & Video Support
Final Data Sheet Rev. 9
GENDOC-047479 September 2013
www.semtech.com
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