GS2970 Datasheet, PDF (90/145 Pages) Semtech Corporation – 3Gb/s, HD, SD SDI Receiver Complete with SMPTE Audio and Video Processing

4.20 GSPI - HOST Interface
The GSPI, or Gennum Serial Peripheral Interface, is a 4-wire interface provided to allow
the system to access additional status and control information through configuration
registers in the GS2970.
The GSPI is comprised of 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 are shared with the JTAG interface port, 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 must be provided by the
system. 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.
See Section 4.20.2 for details. The interface is illustrated in the Figure 4-45 below.
Application Host
SCLK
CS1
SDOUT
GS2970
SCLK
CS
SDIN
SDOUT
CS2
SDIN
GS2970
SCLK
CS
SDIN
SDOUT
Figure 4-45: GSPI Application Interface Connection
All read or write access to the GS2970 is initiated and terminated by the system host
processor. Each access always begins with a Command/Address Word, followed by a
data write to, or data read from, the GS2970.
4.20.1 Command Word Description
The Command Word consists of a 16-bit word transmitted MSB first and contains a
read/write bit, an Auto-Increment bit and a 12-bit address.
MSB
LSB
R/W RSV RSV AutoInc A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
Figure 4-46: Command Word Format
GS2970 3Gb/s, HD, SD SDI Receiver Complete with
SMPTE Audio and Video Processing
Data Sheet
47478 - 4
September 2012
90 of 145