Cycle reference chart: Difference between revisions

From NESdev Wiki
Jump to navigationJump to search
(Updates PAL OAM write window to match newest findings. Exchanges 'even/odd' cycle terminology for 'get/put'.)
m (→‎Clock rates: someone found "every other" insufficiently clear)
 
(4 intermediate revisions by the same user not shown)
Line 12: Line 12:
! NTSC (2C02)
! NTSC (2C02)
! PAL (2C07)
! PAL (2C07)
! Dendy
! "Dendy" PAL Famiclone
! RGB (2C03)
! RGB (2C03/4/5)
! RGB (Vs. 4)
! Brazil Famiclone
! RGB (2C05)
! Argentina Famiclone
|-
|-
| Master clock speed
| Master clock speed
Line 21: Line 21:
| 26.601712 MHz &plusmn; 50 Hz<br/>26.6017125 MHz by definition
| 26.601712 MHz &plusmn; 50 Hz<br/>26.6017125 MHz by definition
| Like PAL
| Like PAL
| colspan=3 align=center|Like NTSC
| Like NTSC
| 21.453671 MHz<br/>3.067875 GHz ÷ 143 by definition
| 21.492338 MHz<br/>42.984675 MHz ÷ 2 by definition
|-
|-
| CPU
| CPU
Line 27: Line 29:
| Ricoh 2A07
| Ricoh 2A07
| UMC UA6527P
| UMC UA6527P
| colspan=3 align=center|Ricoh 2A03
| Ricoh 2A03
| colspan=2 | UMC UA6527
|-
|-
| CPU clock speed
| CPU clock speed
Line 33: Line 36:
| 26.60~ MHz ÷ 16 = 1.662607 MHz
| 26.60~ MHz ÷ 16 = 1.662607 MHz
| 26.60~ MHz ÷ 15 = 1.773448 MHz
| 26.60~ MHz ÷ 15 = 1.773448 MHz
| colspan=3 align=center|Like NTSC
| Like NTSC
| 21.45~ MHz ÷ 12 = 1.787806 MHz
| 21.49~ MHz ÷ 12 = 1.791028 MHz
|-
|-
| [[APU Frame Counter]] rate
| [[APU Frame Counter]] rate
Line 39: Line 44:
| 50 Hz<ref>nesdev forum post by thefox: http://forums.nesdev.org/viewtopic.php?p=160349#p160349</ref>
| 50 Hz<ref>nesdev forum post by thefox: http://forums.nesdev.org/viewtopic.php?p=160349#p160349</ref>
| 59 Hz<ref>nesdev forum post by Eugene.S: http://forums.nesdev.org/viewtopic.php?p=174970#p174970</ref>
| 59 Hz<ref>nesdev forum post by Eugene.S: http://forums.nesdev.org/viewtopic.php?p=174970#p174970</ref>
| colspan=3 align=center|Like NTSC
| Like NTSC
| colspan=2 | Like NTSC
|-
|-
| PPU
| PPU
Line 45: Line 51:
| Ricoh 2C07
| Ricoh 2C07
| UMC UA6538
| UMC UA6538
| Ricoh 2C03
| Ricoh 2C03, 2C04, 2C05
| Ricoh 2C04-0001 through 2C04-0004
| UMC UA6548
| Ricoh 2C05
| UMC UA6528P
|-
|-
| PPU clock speed
| Master clocks per PPU dot
| 21.477272 MHz ÷ 4
| 4
| 26.601712 MHz ÷ 5
| 5
| Like PAL
| 5
| colspan=3 align=center|Like NTSC
| 4
| colspan=2 align=center|4
|-
|-
| PPU dots per CPU cycle
| PPU dots per CPU cycle
| 3
| 3
| 3.2
| 3.2
| 3
| colspan=4 align=center|Like NTSC
| colspan=3 align=center|Like NTSC
|-
|-
| CPU cycles per scanline
| CPU cycles per scanline
Line 65: Line 71:
| 341 × 5÷16 = 106<sup>9</sup>&frasl;<sub>16</sub>
| 341 × 5÷16 = 106<sup>9</sup>&frasl;<sub>16</sub>
| 341 × 5÷15 = 113<sup>2</sup>&frasl;<sub>3</sub>
| 341 × 5÷15 = 113<sup>2</sup>&frasl;<sub>3</sub>
| colspan=4 align=center|Like NTSC
| colspan=3 align=center|Like NTSC
|-
|-
| Height of picture
| Height of picture
Line 71: Line 77:
| 239 scanlines
| 239 scanlines
| Like PAL
| Like PAL
| colspan="3" align="center"|Like NTSC
| Like NTSC
| thought to be like NTSC
| thought to be like PAL
|-
|-
| Nominal visible picture height (see [[Overscan]])
| Nominal visible picture height (see [[Overscan]])
Line 77: Line 85:
| 268 scanlines
| 268 scanlines
| Like PAL
| Like PAL
| colspan=3 align=center|Like NTSC
| Like NTSC
| Like NTSC
| Like PAL
|-
|-
| "Post-render" blanking lines between end of picture and [[NMI]]
| "Post-render" blanking lines between end of picture and [[NMI]]
Line 83: Line 93:
| 1 scanline
| 1 scanline
| 51 scanlines
| 51 scanlines
| colspan=3 align=center|Like NTSC
| 1 scanline
| 1 scanline
| 51 scanlines
|-
|-
| Length of vertical blanking after NMI
| Length of vertical blanking after NMI
| 20 scanlines (≈ 2273 CPU cycles)
| 20 scanlines (≈ 2273 CPU cycles)
| 70 scanlines (≈ 7459 CPU cycles)
| 70 scanlines (≈ 7459 CPU cycles)
| Like NTSC
| colspan=4 align=center |Like NTSC
| colspan=3 align=center|Like NTSC
|-
|-
| Time during which [[OAM]] can be written
| Time during which [[OAM]] can be written
Line 101: Line 112:
|-
|-
| Total number of dots per frame
| Total number of dots per frame
| 341 × 261 + 340.5 = 89341.5<br/>(pre-render line is one dot shorter in every other frame)
| 341 × 261 + 340.5 = 89341.5<br/>(pre-render line is one dot shorter in every odd frame)
| 341 × 312 = 106392
| 341 × 312 = 106392
| Like PAL
| Like PAL
| colspan=3 align=center| 341 × 262 = 89342
| 341 × 262 = 89342
| unknown<br>either like NTSC or RGB
| Like PAL
|-
|-
| Total number of CPU cycles per frame
| Total number of CPU cycles per frame
Line 110: Line 123:
| 106392 ÷ 3.2 = 33247.5
| 106392 ÷ 3.2 = 33247.5
| 106392 ÷ 3 = 35464
| 106392 ÷ 3 = 35464
| colspan=3 align=center| 89342 ÷ 3 = 29780<sup>2</sup>&frasl;<sub>3</sub>
| 89342 ÷ 3 = 29780<sup>2</sup>&frasl;<sub>3</sub>
| unknown<br>either like NTSC or RGB
| Like PAL famiclone
|-
|-
| Frame rate (vertical scan rate)
| Frame rate (vertical scan rate)
Line 116: Line 131:
| 50.0070 Hz
| 50.0070 Hz
| Like PAL
| Like PAL
| colspan=3 align=center|60.0985 Hz
| 60.0985 Hz
| 60.03 Hz
| 50.5027 Hz
|-
|-
| Color of top border
| Color of top border
Line 125: Line 142:
| Always black ($0E), [[Overscan#PAL|intruding on left and right 2 pixels and top 1 pixel of picture]]
| Always black ($0E), [[Overscan#PAL|intruding on left and right 2 pixels and top 1 pixel of picture]]
| Like PAL<ref>nesdev forum post by Eugene.S: https://forums.nesdev.org/viewtopic.php?p=173764#p173764</ref>
| Like PAL<ref>nesdev forum post by Eugene.S: https://forums.nesdev.org/viewtopic.php?p=173764#p173764</ref>
| colspan="3" align="center" | Like NTSC<ref>nesdev forum post by lidnariq: https://forums.nesdev.org/viewtopic.php?p=179705#p179705</ref>
| Like NTSC<ref>nesdev forum post by lidnariq: https://forums.nesdev.org/viewtopic.php?p=179705#p179705</ref>
| Unknown
| Unknown, probably like PAL
|-
|-
| Color emphasis<br/>(with correlating bit in [[PPUMASK]])
| Color emphasis<br/>(with correlating bit in [[PPUMASK]])
Line 131: Line 150:
| Blue (D7), red (D6), green (D5)
| Blue (D7), red (D6), green (D5)
| Like PAL
| Like PAL
| colspan=3 align=center|Blue, green, red (full scale)
| Blue, green, red (full scale)
| colspan=2|Unknown
|-
|-
| Other quirks
| Other quirks
Line 137: Line 157:
|
|
|
|
| Missing $2D and $3D greys
| Many
| Permuted palette
| colspan=2| poorly-researched
| [[PPUCTRL]] and [[PPUMASK]] are swapped; revision ID in [[PPUSTATUS]] (D4-D0)
|}
|}
Some frequencies in the above table are rounded.
Some frequencies in the above table are rounded.

Latest revision as of 19:36, 26 August 2024

Clock rates

The clock rate of various components in the NES differs between consoles in the USA and Europe due to the different television standards used (NTSC M vs. PAL B). The color encoding method used by the NES (see NTSC video) requires that the master clock frequency be six times that of the color subcarrier, but this frequency is about 24% higher on PAL than on NTSC. In addition, PAL has more scanlines per field and fewer fields per second than NTSC. Furthermore, the PAL CPU's master clock could have been divided by 15 to preserve the ratio between CPU and PPU speeds, but Nintendo chose to keep the Johnson counter structure, which always has an even period, and divide by 16 instead.

So the main differences between the NTSC and PAL PPUs are depicted in the following table:

Property NTSC (2C02) PAL (2C07) "Dendy" PAL Famiclone RGB (2C03/4/5) Brazil Famiclone Argentina Famiclone
Master clock speed 21.477272 MHz ± 40 Hz
236.25 MHz ÷ 11 by definition
26.601712 MHz ± 50 Hz
26.6017125 MHz by definition
Like PAL Like NTSC 21.453671 MHz
3.067875 GHz ÷ 143 by definition
21.492338 MHz
42.984675 MHz ÷ 2 by definition
CPU Ricoh 2A03 Ricoh 2A07 UMC UA6527P Ricoh 2A03 UMC UA6527
CPU clock speed 21.47~ MHz ÷ 12 = 1.789773 MHz 26.60~ MHz ÷ 16 = 1.662607 MHz 26.60~ MHz ÷ 15 = 1.773448 MHz Like NTSC 21.45~ MHz ÷ 12 = 1.787806 MHz 21.49~ MHz ÷ 12 = 1.791028 MHz
APU Frame Counter rate 60 Hz 50 Hz[1] 59 Hz[2] Like NTSC Like NTSC
PPU Ricoh 2C02 Ricoh 2C07 UMC UA6538 Ricoh 2C03, 2C04, 2C05 UMC UA6548 UMC UA6528P
Master clocks per PPU dot 4 5 5 4 4
PPU dots per CPU cycle 3 3.2 Like NTSC
CPU cycles per scanline 341 × 4÷12 = 11323 341 × 5÷16 = 106916 341 × 5÷15 = 11323 Like NTSC
Height of picture 240 scanlines 239 scanlines Like PAL Like NTSC thought to be like NTSC thought to be like PAL
Nominal visible picture height (see Overscan) 224 scanlines 268 scanlines Like PAL Like NTSC Like NTSC Like PAL
"Post-render" blanking lines between end of picture and NMI 1 scanline 1 scanline 51 scanlines 1 scanline 1 scanline 51 scanlines
Length of vertical blanking after NMI 20 scanlines (≈ 2273 CPU cycles) 70 scanlines (≈ 7459 CPU cycles) Like NTSC
Time during which OAM can be written Vertical or forced blanking Only during first 24 scanlines after NMI (≈2557 CPU cycles) Like NTSC Like NTSC
"Pre-render" lines between vertical blanking and next picture 1 scanline
Total number of dots per frame 341 × 261 + 340.5 = 89341.5
(pre-render line is one dot shorter in every odd frame)
341 × 312 = 106392 Like PAL 341 × 262 = 89342 unknown
either like NTSC or RGB
Like PAL
Total number of CPU cycles per frame 89341.5 ÷ 3 = 29780.5 106392 ÷ 3.2 = 33247.5 106392 ÷ 3 = 35464 89342 ÷ 3 = 2978023 unknown
either like NTSC or RGB
Like PAL famiclone
Frame rate (vertical scan rate) 60.0988 Hz 50.0070 Hz Like PAL 60.0985 Hz 60.03 Hz 50.5027 Hz
Color of top border Always black ($0E)
Side and bottom borders Palette entry at $3F00 Always black ($0E), intruding on left and right 2 pixels and top 1 pixel of picture Like PAL[3] Like NTSC[4] Unknown Unknown, probably like PAL
Color emphasis
(with correlating bit in PPUMASK)
Blue (D7), green (D6), red (D5) Blue (D7), red (D6), green (D5) Like PAL Blue, green, red (full scale) Unknown
Other quirks Early revisions cannot read back sprite or palette memory Many poorly-researched

Some frequencies in the above table are rounded.

The 2C03, 2C04, and 2C05 PPUs were all found in Nintendo's Vs. System and PlayChoice-10 (a.k.a. PC10 or PC-10) arcade systems. Famicom Titler, Famicom TVs, and RGB-modded NES consoles would use either the 2C03 or a 2C05 with glue logic to unswap $2000 and $2001. (Later RGB mods used a 2C02 in output mode and faked out all palette logic.)

The color emphasis bits on the PAL NES have their red and green bits in PPUMASK swapped

The authentic NES sold in Brazil is an NTSC NES with an adapter board to turn the NTSC video into PAL-M video, a variant of PAL using NTSC frequencies but PAL's color modulation.

Micro Genius is a clone of the Famicom, manufactured by TXC Corporation of Taiwan and sold under various brand names in the 50 Hz market.[5] Among the best known brands is Dendy, distributed in Russia by Steepler, and the attention given by Russian reverse engineers to this clone has led to "Dendy" becoming a common name for all PAL Micro Genius-type famiclones. Its chipset (UA6527P+UA6538) is designed for compatibility with Famicom games, including games with CPU cycle counting mappers (e.g. VRC4) and games that use a cycle-timed NMI handler (e.g. Balloon Fight). This explains the faster CPU divider and longer post-render period vs. the authentic PAL NES.

To compensate for these differences, you can detect the TV system at power-on.

CPU cycle counts

To make things easier for those programming on the NES, the below chart provides the number of CPU cycles that a particular PPU-oriented trait takes.

Property NTSC PAL Dendy
Scanline (341 pixels) 11323 106916 11323
HBlank (85 pixels) 2813 26916 2813
NMI to start of rendering 227313 745938 227313
Frame 29780.5* 33247.5 35464
PPU dots ÷ CPU cycles 3 3.2 3
OAM DMA 513 (+1 if starting on CPU get cycles)

* NTSC frame timing is 29780.5 cycles if rendering is enabled during the 20th scanline; 2978023 otherwise.

See also

References