Playfield Timing Diagram
Timing Tables
The following tables show the latest cycles at which you can write to the playfield registers, for each individual playfield pixel (as well as the beginning of HBLANK). The first two tables show how the numbers are determined, and the last table presents the numbers in a compact format.
The first two tables use four special characters-- the division symbol, as well as superscripts 0, 1, and 2-- so you need a font with those characters in it (which should be just about any fixed-spacing font). "Courier New" is fine, but I think "Lucida Console" looks best. The superscripted numbers represent thirds, for remainders, so a superscript of 0 is "no-thirds" (or no remainder), a superscript of 1 is "one-third" (or a remainder of 1), and a superscript of 2 is "two-thirds" (or a remainder of 2). The first table shows the calculations for a repeated playfield, and the second table shows the calculations for a reflected playfield.
Following is an explanation of what the first set of tables are showing. The first row shows the color clock where each playfield pixel begins. We divide by 3 to get the machine cycle, but there could be a remainder of 1 or 2, so the third row shows the result of the division along with the remainder (0, 1, or 2). Then we subtract 2/3 of a cycle to allow for the delay, so the fifth row shows the result of the subtraction along with the fractional part. Then we drop any fractional part to get the final result in the seventh row.
Why do the tables for each individual playfield pixel? Well, 99% of the time you'd want the new value of a playfield register to be displayed in its entirety. But if you're ever in a situation where it would be okay to update a playfield a little earlier or later than usual-- because you aren't using some of the leftmost or rightmost pixels of that playfield register-- then you might want to get down to the pixel level.
Also, the values for the last pixel of each playfield register determine the *earliest* you can update that playfield register for its next copy. For example, if you're using a repeated playfield, the left copy of PF0 must be updated no later than cycle 22, otherwise the display will be "corrupted," combining a little bit of the old value of PF0 with the new value of PF0. Similarly, the earliest you could update PF0 again without displaying part of the new value is cycle 27. For the right copy of PF0, the latest cycle to display the new value is cycle 48, and the earliest you could update PF0 again is cycle 53. So if you put those together, you see that (when using a repeated playfield) the value for the left copy of PF0 must be written between cycle 53 (of the previous scan line) and cycle 22 (of the current scan line), whereas the value for the right copy of PF0 must be written between cycle 27 and cycle 48.
You can also see what would happen if you update a playfield register at an oddball or "incorrect" time. For example, if you write a new value to PF1 at cycle 33, the first five pixels of the left copy of PF1 will show the old value, and the last three pixels of the left copy of PF1 will show the new value.
Just to be sure, these cycle numbers represent the next cycle after the write instruction has finished. For example, "STA PF1" takes 3 cycles, so if the instruction begins on cycle 28, it will span cycles 28, 29, and 30, hence the next cycle after the write instruction has finished will be cycle 31.
. Repeated Playfield: ================= | HBLANK | 000 | | | ÷ 3 | | | 00º | | | - ² | | | 75¹ | | |------| | | 75 | ====================================== | L. PF0 | 068 | 072 | 076 | 080 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 22² | 24º | 25¹ | 26² | | | - ² | - ² | - ² | - ² | | | 22º | 23¹ | 24² | 26º | | |------|------|------|------| | | 22 | 23 | 24 | 26 | ================================================================== | L. PF1 | 084 | 088 | 092 | 096 | 100 | 104 | 108 | 112 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 28º | 29¹ | 30² | 32º | 33¹ | 34² | 36º | 37¹ | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 27¹ | 28² | 30º | 31¹ | 32² | 34º | 35¹ | 36² | | |------|------|------|------|------|------|------|------| | | 27 | 28 | 30 | 31 | 32 | 34 | 35 | 36 | ================================================================== | L. PF2 | 116 | 120 | 124 | 128 | 132 | 136 | 140 | 144 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 38² | 40º | 41¹ | 42² | 44º | 45¹ | 46² | 48º | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 38º | 39¹ | 40² | 42º | 43¹ | 44² | 46º | 47¹ | | |------|------|------|------|------|------|------|------| | | 38 | 39 | 40 | 42 | 43 | 44 | 46 | 47 | ================================================================== | R. PF0 | 148 | 152 | 156 | 160 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 49¹ | 50² | 52º | 53¹ | | | - ² | - ² | - ² | - ² | | | 48² | 50º | 51¹ | 52² | | |------|------|------|------| | | 48 | 50 | 51 | 52 | ================================================================== | R. PF1 | 164 | 168 | 172 | 176 | 180 | 184 | 188 | 192 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 54² | 56º | 57¹ | 58² | 60º | 61¹ | 62² | 64º | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 54º | 55¹ | 56² | 58º | 59¹ | 60² | 62º | 63¹ | | |------|------|------|------|------|------|------|------| | | 54 | 55 | 56 | 58 | 59 | 60 | 62 | 63 | ================================================================== | R. PF2 | 196 | 200 | 204 | 208 | 212 | 216 | 220 | 224 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 65¹ | 66² | 68º | 69¹ | 70² | 72º | 73¹ | 74² | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 64² | 66º | 67¹ | 68² | 70º | 71¹ | 72² | 74º | | |------|------|------|------|------|------|------|------| | | 64 | 66 | 67 | 68 | 70 | 71 | 72 | 74 | ================================================================== Reflected Playfield: ================= | HBLANK | 000 | | | ÷ 3 | | | 00º | | | - ² | | | 75¹ | | |------| | | 75 | ====================================== | L. PF0 | 068 | 072 | 076 | 080 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 22² | 24º | 25¹ | 26² | | | - ² | - ² | - ² | - ² | | | 22º | 23¹ | 24² | 26º | | |------|------|------|------| | | 22 | 23 | 24 | 26 | ================================================================== | L. PF1 | 084 | 088 | 092 | 096 | 100 | 104 | 108 | 112 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 28º | 29¹ | 30² | 32º | 33¹ | 34² | 36º | 37¹ | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 27¹ | 28² | 30º | 31¹ | 32² | 34º | 35¹ | 36² | | |------|------|------|------|------|------|------|------| | | 27 | 28 | 30 | 31 | 32 | 34 | 35 | 36 | ================================================================== | L. PF2 | 116 | 120 | 124 | 128 | 132 | 136 | 140 | 144 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 38² | 40º | 41¹ | 42² | 44º | 45¹ | 46² | 48º | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 38º | 39¹ | 40² | 42º | 43¹ | 44² | 46º | 47¹ | | |------|------|------|------|------|------|------|------| | | 38 | 39 | 40 | 42 | 43 | 44 | 46 | 47 | ================================================================== | R. PF2 | 148 | 152 | 156 | 160 | 164 | 168 | 172 | 176 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 49¹ | 50² | 52º | 53¹ | 54² | 56º | 57¹ | 58² | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 48² | 50º | 51¹ | 52² | 54º | 55¹ | 56² | 58º | | |------|------|------|------|------|------|------|------| | | 48 | 50 | 51 | 52 | 54 | 55 | 56 | 58 | ================================================================== | R. PF1 | 180 | 184 | 188 | 192 | 196 | 200 | 204 | 208 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 60º | 61¹ | 62² | 64º | 65¹ | 66² | 68º | 69¹ | | | - ² | - ² | - ² | - ² | - ² | - ² | - ² | - ² | | | 59¹ | 60² | 62º | 63¹ | 64² | 66º | 67¹ | 68² | | |------|------|------|------|------|------|------|------| | | 59 | 60 | 62 | 63 | 64 | 66 | 67 | 68 | ================================================================== | R. PF0 | 212 | 216 | 220 | 224 | | | ÷ 3 | ÷ 3 | ÷ 3 | ÷ 3 | | | 70² | 72º | 73¹ | 74² | | | - ² | - ² | - ² | - ² | | | 70º | 71¹ | 72² | 74º | | |------|------|------|------| | | 70 | 71 | 72 | 74 | ====================================== .
This next table is the more compacted version. I've been told that some consoles (e.g., the Coleco Gemini) have a delay of 1 full machine cycle, rather than the usual delay of 2/3 of a machine cycle, so this compacted table shows the timing values for both delays. In most cases the values are the same, due to different remainders being rounded down to the same whole value. But there are places where the values are different, and those places are marked with an asterisk.
In this last table, the first column is for a repeated playfield. The numbers after the dashes represent pixel numbers, not bit numbers. For example, "LPF0-0" means "left copy of PF0, pixel 0" (where the pixels are numbered from 0 to 7 from left to right across the screen). The second column is for a reflected playfield. The third column shows the screen position in color clocks, numbered from 0 to 159 (with HBLANK being -68 to -1). The fourth column shows the scan line position in color clocks, numbered from 0 to 227. The fifth column shows the latest machine cycle when you can update a playfield pixel and have the new value be displayed, assuming the standard delay of 2/3 of a machine cycle. The sixth column shows the latest machine cycle for nonstandard consoles where the delay is 1 machine cycle, with an asterisk by the places where this value is different than the fifth column.
. repeatd reflectd posit clock -2/3 -1 ======================================= HBLANK | HBLANK | -68 | 000 | 75 | 75 --------------------------------------- LPF0-0 | LPF0-0 | 000 | 068 | 22 | 21 * LPF0-1 | LPF0-1 | 004 | 072 | 23 | 23 LPF0-2 | LPF0-2 | 008 | 076 | 24 | 24 LPF0-3 | LPF0-3 | 012 | 080 | 26 | 25 * LPF1-0 | LPF1-0 | 016 | 084 | 27 | 27 LPF1-1 | LPF1-1 | 020 | 088 | 28 | 28 LPF1-2 | LPF1-2 | 024 | 092 | 30 | 29 * LPF1-3 | LPF1-3 | 028 | 096 | 31 | 31 LPF1-4 | LPF1-4 | 032 | 100 | 32 | 32 LPF1-5 | LPF1-5 | 036 | 104 | 34 | 33 * LPF1-6 | LPF1-6 | 040 | 108 | 35 | 35 LPF1-7 | LPF1-7 | 044 | 112 | 36 | 36 LPF2-0 | LPF2-0 | 048 | 116 | 38 | 37 * LPF2-1 | LPF2-1 | 052 | 120 | 39 | 39 LPF2-2 | LPF2-2 | 056 | 124 | 40 | 40 LPF2-3 | LPF2-3 | 060 | 128 | 42 | 41 * LPF2-4 | LPF2-4 | 064 | 132 | 43 | 43 LPF2-5 | LPF2-5 | 068 | 136 | 44 | 44 LPF2-6 | LPF2-6 | 072 | 140 | 46 | 45 * LPF2-7 | LPF2-7 | 076 | 144 | 47 | 47 --------------------------------------- RPF0-0 | RPF2-0 | 080 | 148 | 48 | 48 RPF0-1 | RPF2-1 | 084 | 152 | 50 | 49 * RPF0-2 | RPF2-2 | 088 | 156 | 51 | 51 RPF0-3 | RPF2-3 | 092 | 160 | 52 | 52 RPF1-0 | RPF2-4 | 096 | 164 | 54 | 53 * RPF1-1 | RPF2-5 | 100 | 168 | 55 | 55 RPF1-2 | RPF2-6 | 104 | 172 | 56 | 56 RPF1-3 | RPF2-7 | 108 | 176 | 58 | 57 * RPF1-4 | RPF1-0 | 112 | 180 | 59 | 59 RPF1-5 | RPF1-1 | 116 | 184 | 60 | 60 RPF1-6 | RPF1-2 | 120 | 188 | 62 | 61 * RPF1-7 | RPF1-3 | 124 | 192 | 63 | 63 RPF2-0 | RPF1-4 | 128 | 196 | 64 | 64 RPF2-1 | RPF1-5 | 132 | 200 | 66 | 65 * RPF2-2 | RPF1-6 | 136 | 204 | 67 | 67 RPF2-3 | RPF1-7 | 140 | 208 | 68 | 68 RPF2-4 | RPF0-0 | 144 | 212 | 70 | 69 * RPF2-5 | RPF0-1 | 148 | 216 | 71 | 71 RPF2-6 | RPF0-2 | 152 | 220 | 72 | 72 RPF2-7 | RPF0-3 | 156 | 224 | 74 | 73 * --------------------------------------- .
Earliest/Latest Write Timing
. Asymmetrical Playfield, Repeated Graphics (PF0-PF1-PF2-PF0-PF1-PF2): ============================================== | Playfield Register | Earliest | Latest | ============================================== | Left copy of PF0 | Cycle 53 * | Cycle 21 | | Left copy of PF1 | Cycle 64 * | Cycle 27 | | Left copy of PF2 | Cycle 75 * | Cycle 37 | | Right copy of PF0 | Cycle 27 | Cycle 48 | | Right copy of PF1 | Cycle 37 | Cycle 53 | | Right copy of PF2 | Cycle 48 | Cycle 64 | ============================================== Asymmetrical Playfield, Reflected Graphics (PF0-PF1-PF2-PF2-PF1-PF0): ============================================== | Playfield Register | Earliest | Latest | ============================================== | Left copy of PF0 | Cycle 75 * | Cycle 21 | | Left copy of PF1 | Cycle 69 * | Cycle 27 | | Left copy of PF2 | Cycle 59 * | Cycle 37 | | Right copy of PF2 | Cycle 48 | Cycle 48 | | Right copy of PF1 | Cycle 37 | Cycle 59 | | Right copy of PF0 | Cycle 27 | Cycle 69 | ============================================== * = This refers to a cycle on the previous scan line. .
If the left and right copies will be the same (i.e., a non-asymmetric playfield), use the cycle numbers listed for the left copies.
Note that most of the playfield registers have a good bit of leeway as to when they can be written to. The exception to this is the right copy of PF2 when drawing an asymmetrical playfield using reflected graphics-- the value for the right copy *must* be written to PF2 on cycle 48, no ifs, ands, or buts!