GS1531 Data Sheet
30573 - 7 February 2008 40 of 50
Figure 4-4: Serial Digital Output Swing
4.9.2 Serial Digital Output Mute
The GS1531 will automatically mute the serial digital output when the LOCKED
output signal is LOW. In this case, the SDO and SDO
signals are set to a constant
voltage level.
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.
50Ω load
300
400
500
600
700
800
900
1000
250
300
350
400
450
500
550
600
650
700
RSET(Ω)
ΔV
SDO
(mVp-p)
200
75Ω load
