Overclocking X1900s with ATITool is almost the same as any other card. However, there are a few more options that come into play - these mainly being voltages and some other features of the card.
On the main menu of ATITool, there are a few additional measurements for the X1900 as listed below.
1. Voltage Regulator Temperature (Celsius)
2. GPU Current Draw (Amperes)
3. Fan Speed (Percentage)
4. GPU Temperature (Celsius)
5. Temperature of Temp Chip (Celsius)
Core/PCB temperature is always a great help with overclocking; but now there is a reading for the Voltage Regulators. There is also a read for current draw on the GPU. This can come in handy to see how much power your card is pulling, and if it's too much for your PSU.
Under "Overclocking" the Device Properties are found. Again, with this, everything is pretty much the same besides the values for Device ID and such. Fan Control is also the same.
X1900XT Device Properties & Fan Control
Voltages
Another great improvement on the X1900 series card is the ability to control the card's voltages by software. ATITool has an option menu for this, with four voltages that can be controlled. This one of the major changes in ATITool under the "Settings" menu.
- VGPU - This controls the voltage the goes the GPU or the core as it is sometimes called.
- MVDDC - This setting controls the voltage to the memory.
- MVDDQ - This setting controls the voltage on the memory output buffers.
- VDDCI - Controls additional voltage on the GPU with the X1900s.
After you have successfully disabled the HotKey Poller service, or you just let ATITool end running instances of Ati2evxx.exe and you understand how to use ATITool, you're ready to begin overclocking. As mentioned before, you will be running at 2D speeds, which are reduced. Don't worry about this. Simply set the voltage on the core, then bring the core and memory frequencies up to the 3D speeds according to your card (XT or XTX).
Default 2D clocks/voltages
To get the card running at 3D clocks, go into the voltage section found under "Settings" and bring the VGPU voltage to 1.425v. The other voltages (MVDDC, MVDDQ, and VDDCI) are the same for 2D/3D modes. After setting the voltages, bring the core/memory frequency up to the default of your card (XT - 625/725, XTX - 650/775). Then save these settings as a profile called 3D Clocks, or similar (make sure you check voltages when saving the profile).
Default 3D clocks/voltages