GENNUM CORPORATION
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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 GS9060.
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.
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 14.
All read or write access to the GS9060 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.
Figure 14 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 GS9060 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
0
in
Figure 17 and Figure 18) before the first clock edge to
ensure proper operation.
Each command word must be followed by only one data
word to ensure proper operation.
Figure 15 Command Word
Figure 16 Data Word
SCLK
CS
SDOUT
SDIN
SCLK
CS
SDIN
SDOUT
Application Host
GS9060
R/W
RSV
RSV
RSV
A0
A1
A2
A3
A4
A5
RSV
RSV
RSV
RSV
RSV
RSV
MSB
LSB
D15
D14
D13
D12
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D11
D10
MSB
LSB