GS4901B Datasheet, PDF (63/95 Pages) Gennum Corporation – SD Clock and Timing Generator with GENLOCK

GS4901B/GS4900B Preliminary Data Sheet
3.10 GSPI Host Interface
The GSPI, or Gennum Serial Peripheral Interface, is a 4-wire interface provided to
allow the host to enable additional features of the GS4901B/GS4900B and/or to
provide additional status information through configuration registers in the device.
The GSPI comprises a serial data input signal, SDIN, a serial data output signal,
SDOUT, an active low chip select, CS, and a burst clock, SCLK. The burst clock
must have a duty cycle between 40% and 60%.
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 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 pin of another device, allowing multiple devices
to be connected to the GSPI chain. The interface is illustrated in Figure 3-11.
Application Host
SCLK
CS1
SDOUT
GS4911B/GS4910B
SCLK
CS
SDIN
SDOUT
CS2
SDIN
GS4911B/GS4910B
SCLK
CS
SDIN
SDOUT
Figure 3-11: GSPI Application Interface Connection
All read or write access to the GS4901B/GS4900B is initiated and terminated by
the host processor. Each access always begins with a 16-bit command word on
SDIN indicating the address of the register of interest. This is followed by a 16-bit
data word on SDIN in write mode, or a 16-bit data word on SDOUT in read mode.
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