GM2121 Datasheet, PDF (19/51 Pages) List of Unclassifed Manufacturers – SXGA LCD Monitor Controller with Integrated Analog Interface and Dual LVDS Transmitter

gm2121 Preliminary Data Sheet
Some attention must be given to the details of the oscillator circuit when used with a crystal resonator.
The PCB traces should be as short as possible. The value of C_load that is specified by the manufacturer
should not be exceeded because of potential start up problems with the oscillator. Additionally, the crystal
should be a parallel resonate-cut and the value of the equivalent series resistance must be less then 90
Ohms.
4.1.2 Using an External Clock Oscillator
Another option for providing the reference clock is to use a single-ended external clock oscillator. When
the gm2121 is in reset, the state of the ROM_ADDR13 is sampled. If ROM_ADDR13 is pulled high by
connecting to VDD through a pull-up resistor (10KΩ recommended, 15KΩ maximum) then external
oscillator mode is enabled. In this mode the internal oscillator circuit is disabled and the external
oscillator signal that is connected to the TCLK pin is routed to an internal clock buffer. This is illustrated
in Figure 7.
Vdd
14 to 24 MHz
Vdd
Oscillator
GND
Vdd
102
TCLK
103
XTAL
10 K
141
ROM_ADDR13
gm2121
Internal
Oscillator
Disable
OSC_OUT
TCLK Distribution
Reset State Logic
Internal Pull Down
Resistor
~ 60 K
External Oscillator Enable
Figure 7.
Using an External Single-ended Clock Oscillator
Table 11.
Frequency
Jitter Tolerance
Rise Time (10% to 90%)
Maximum Duty Cycle
TCLK Specification
14 to 24 MHz
250 ps
5 ns
40-60
C2121-DAT-01F
19
http://www.genesis-microchip.com
December 2002