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
Application Host
GS4911B/GS4910B
SCLK
CS1
SDOUT
SCLK
CS
SDIN
SDOUT
GS4911B/GS4910B
SCLK
CS2
CS
SDIN
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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April 2006
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