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Screen update - can you turn it off


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Yes, VDP write-only register 1. The default for register 1 is >EO in the Editor/Assembler, TI BASIC, and TI Extended BASIC. Before changing this register, put a copy of the new value you wish it to have at address >83D4. When a key is pressed, a copy of the value at this address is placed in register 1. Bit 1 is blank enable/disable. A value of 0 causes the active display (the entire screen) to be blank, and a value of 1 allows display on the screen. With a value of 0, the screen only shows the border color.

 

ref.: E/A-manual page 326.

Edited by sometimes99er
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Is there any performance gain by turning off the screen? I have seen on other systems where, when doing so, the video processor does not have to fetch data from RAM thus giving a slight increase in speed. Of course, with the wait-states injected into the system, turning off the screen may be moot.

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Is there any performance gain by turning off the screen? I have seen on other systems where, when doing so, the video processor does not have to fetch data from RAM thus giving a slight increase in speed. Of course, with the wait-states injected into the system, turning off the screen may be moot.

 

Nope, the CPU does not share a bus with the VDP RAM, so there's no intrinsic performance gain. However, while the screen is blanked, all VDP cycles are RAM access cycles, which means you do not need delays between reads/writes to VRAM. (However, on a stock 99/4A it's rather difficult to overrun the VDP anyway, there are only a couple of cases where it's possible).

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Nope, the CPU does not share a bus with the VDP RAM, so there's no intrinsic performance gain. However, while the screen is blanked, all VDP cycles are RAM access cycles, which means you do not need delays between reads/writes to VRAM. (However, on a stock 99/4A it's rather difficult to overrun the VDP anyway, there are only a couple of cases where it's possible).

 

Yes, I should have known that. Thanks :)

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