GS1560A/GS1561 Data Sheet
3.12 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
GS1560A/GS1561.
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 Figure 3-9.
All read or write access to the GS1560A/GS1561 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
GS1560A / GS1561
SCLK
SDOUT
SDIN
CS
CS
SDIN
SDOUT
Figure 3-9: Gennum Serial Peripheral Interface (GSPI)
3.12.1 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 GS1560A/GS1561 on the rising edge of the
serial clock SCLK. The appropriate chip select, CS, signal must be asserted low a
minimum of 1.5ns (t in Figure 3-12 and Figure 3-13) before the first clock edge to
0
ensure proper operation.
Each command word must be followed by only one data word to ensure proper
operation.
27360 - 8 September 2005
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GENNUM [ GENNUM CORPORATION ]
