GS1531 Data Sheet
4.10 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 device and /or to provide
additional status information through configuration registers in the GS1531.
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. 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 host interface. The SDOUT pin is a high-impedance output allowing multiple
devices to be connected in parallel and selected via the CS input. The interface is
illustrated in the Figure 4-5 below.
All read or write access to the GS1531 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.
Application Host
SCLK
GS1531
SCLK
SDIN
SDOUT
CS
CS
SDIN
SDOUT
Figure 4-5: Gennum Serial Peripheral Interface (GSPI)
4.10.1 Command Word Description
The command word is transmitted MSB first and contains a read/write bit, nine
reserved bits and a 6-bit register address. Set R/W = '1' to read and R/W = '0' to
write from the GSPI.
Command words are clocked into the GS1531 on the rising edge of the serial clock
SCLK. The appropriate chip select signal, CS, must be asserted low a minimum of
1.5ns (t0 in Figure 4-8 and Figure 4-9) before the first clock edge to ensure proper
operation.
Each command word must be followed by only one data word to ensure proper
operation.
30573 - 4 July 2005
40 of 49
GENNUM [ GENNUM CORPORATION ]
