What's Prefill?

[kelvSYC]

What's prefill and why is it only available with number select on in the "add/edit" menu, and only 00 and 01 (not FF) at that?

[Pugsy]

Prefill was one of my ideas....if you look at the metrocross 'Select starting round' cheat you will see what it will achieve. Basically it pre-pokes a location with a value (it's normally going to be FF btw) and it then starts to look at that location for a change before poking it again (Old Cheat Type 06X). A game will often poke the level location twice during the start sequence so a 06X cheat on it's own won't do the trick and a constant poke will meant that you have to turn the cheat off after the game has started and that in itself could lead to some nasty side effects.

[kelvSYC]

So it's like applying two cheats, one type 00000000 and the second type 00000002, in order then?

[ianpatt]

Here's a step-by-step list for what the cheat engine does:

1. Write the prefill value.
2. Wait until the value is changed to something else.
3. Do the rest of the cheat as normal.

[Pugsy]

So it's like applying two cheats, one type 00000000 and the second type 00000002, in order then?

Nope it's not like that at all, let me trying explaining it in another way.

A prefill coupled with a select cheat will work thus:-

1. Poke the location once and remove from the active list (old type 001)

2. It will then continue peeking the location and look for a change from the value poked in step 1 before progressing to step 3.

3. It will then poke it with the new value.

It's important that at step 2 we use a value which would not normally be seen in the 'wild' so 'FF' is going to be used 99% of the time. 00 & 01 have a few applications for when FF doesn't work.. Eg poking FF may cause undesirable effects if it's out of range for that location in which case we poke whatever is NOT the first level value.

Eg. Where Level 1 = 01 and we want to start on level 3

On 'Press 1 or 2 Player screen', Level Location Value = 01
New Value = FF
It would then wait till the value changes from FF = WAITS!!
You press 1 or 2 to start the game and the value now = 01
It would then see the new value and then poke it straight away = 03
The game starts on level 3


NOTE, this is different from:-

1. Poke the location once and remove from the active list (old type 001)

2. It will then continue peeking the location and look for a change

3. It will then poke it with the new value.

This won't work as step 2 will not be aware of step 1, as the cheat engine will poke all values at once.

Eg. Where Level 1 = 01 and we want to start on level 3

On 'Press 1 or 2 Player screen', Level Location Value = 01
New Value = FF
It would then see the new value and then poke it straight away = 03
You press 1 or 2 to start the game and the value now = 01
The cheat has already delivered it's payload so nothing will happen! = STILL = 01
The game starts on level 1