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Television Specification (NTSC, PAL, etc.)

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Stephen Illingworth edited this page Jan 13, 2024 · 2 revisions

Gopher2600 supports the following TV specifications

  • NTSC (53.10Hz to 60.05Hz and higher)
  • PAL (50.43Hz to 52.10Hz)
  • SECAM
  • PAL-M

The assumed television specification is NTSC but if the frame generated by the emulated console drops below 52Hz, the equivalent of 302 scanlines, the specification will automatically change to PAL.

It is possible to have a PAL signal with a refresh rate greater than 60Hz but in that case the TV specification needs to be stated explicitly.

Changing the TV Specification

There are two key ways to indicate what TV specification is to be used. (a) on the command line when starting the emulator; and (b) via the file name of the ROM.

From the command line, the command line argument is -tv and applies to most modes. For example:

gopher2600 -tv pal roms/Pitfall.bin

Or:

gopher2600 debug -tv pal roms/Pitfall.bin

The second way is to "embed" the TV specification in the filename of the ROM. Examples are the best way of illustrating this:

Pitfall_PAL.bin
Yars' Revenge (Time Freeze) (1982) (Atari, Howard Scott Warshaw) (CX2655, CX2655P) (PAL).bin
galaga_dmo_v2_PAL60.bin

Note that if the TV specification is explicitly stated, either via the command line or by the filename, the automatic switch (described in the second paragraph above) between PAL and NTSC will no longer occur.

PAL60 and PAL-M

In addition to the four TV specifications listed at the top of this page, Gopher2600 also recognises PAL60. This is in fact a synonym for PAL but it implies that the TV frame will be running closer to 60Hz than to 50Hz.

PAL-M is a little bit different (see following sub-section) but from the end users points of view, PAL-M produces the same palette of colours as NTSC.

Effect on the Emulated Console

The selected TV specification also sets the clock speed of the emulated console. This is rarely anything that needs to concern the user of either a real hardware console or an emulated console. None-the-less, the complete list of clock speeds for each TV specification is listed below.

NTSC 1.193182 Mhz
PAL 1.182298 Mhz
SECAM 1.187500 Mhz
PAL-M 1.191870 Mhz

As stated in the previous section, a PAL60 system is the same as a PAL system - meaning that PAL60 runs with a clock speed of 1.18Mhz.

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