![](http://datasheet.mmic.net.cn/390000/TVP3010C_datasheet_16839161/TVP3010C_23.png)
2–7
Internally, RCLK, SCLK, and VCLK are generated from a common clock counter that is counted at the rising
edge of the dot clock. Therefore, when VCLK is enabled, it is naturally in phase with RCLK and SCLK as
shown in Figure 2–1.
Normally, the video-control signal inputs HSYNC, VSYNC, and SYSBL are latched on the falling edge of
VCLK when in a non-VGA mode. When the configuration register is programmed for opposite VCLK polarity,
these video-control signals are latched on the rising edge of VCLK.
The internal clock counter is initialized any time the output-clock selection register is written with 3F (hex).
This provides a simple mechanism to synchronize multiple palettes or system devices by providing a known
phase relationship for the various system clocks. It is left up to the user to provide some means of disabling
the dot-clock input to the part while this reset is occurring if multiple parts are to be synchronized.
The reset default divide ratio for RCLK is 64:1 with SCLK held low and VCLK held at high. When choosing
certain video timing parameters, exercise caution if the selected RCLK frequency is less than the selected
VCLK frequency (see Appendix B for a more detailed discussion).
Dot Clock
VCLK
(dot clock/4 as an example)
RCLK = SCLK
(dot clock/2 as an example)
Figure 2–1. Dot Clock/VCLK/RCLK/SCLK Relationship
The input-clock-selection register selects the desired input-clock source. Table 2–5 details how to program
the various options.
Table 2–5. Input-Clock Selection Register
INPUT-CLOCK-SELECT REGISTER
(HEX) (see Note 6)
FUNCTION (see Note 7)
00
Select CLK0 as TTL-clock source
01
Select CLK1 as TTL-clock source
02
Select CLK2 as TTL-clock source
03
04
06
07
Select CLK3 as TTL-clock source
Select CLK4 as TTL-clock source
Select CLK3/CLK4 as ECL-clock source up to 140 MHz
Select CLK1/CLK2 as ECL-clock source up to device limit
10
Select CLK0 as doubled TTL-clock source
11
Select CLK1 as doubled TTL-clock source
12
Select CLK2 as doubled TTL-clock source
13
Select CLK3 as doubled TTL-clock source
14
Select CLK4 as doubled TTL-clock source
16
Select CLK3/CLK4 as doubled ECL-clock source
17
Select CLK1/CLK2 as doubled ECL-clock source
CLK0 is chosen at reset as required for VGA pass-through.
NOTES:
6. Register bits 3 and 7 are don’t-care bits.
7. Register bits 5 and 6 are reserved.
8. When the clocks are selected from one input clock source to another, a minimum of 30 ns is needed before
the new clocks are stabilized and running.