Posted By
TLC
on 2011-06-16
15:28:00
|  Re: Plus/4 - PAL/NTSC switchable mod
Vimfuego: yeah, that actually needs some hw hacking, but it's pretty simple. You don't need a different TED chip, they support both tv standards all by themself, yet, you need to do some modifications. If you check the schematic diagram of the Plus/4, you'd find out that PAL machines have a 17.734470MHz crystal, whilst NTSC machines have a 14.31818MHz one. In order to make the machine "switchable", you need to hack in the respective "other" type of crystal + the small trimmer capacitor (you'd use that one to finetune the oscillator frequency) + a switch to select between the crystal circuits. Two things to note: 1.) the TED is capable of producing both PAL and NTSC (off the respective crystal frequency, that is), but, as to which one is set upon booting the machine, is determined by the Kernal ROM. So, in practice, a "switchable" machine would also need some sort of ROM switching (setting a PAL or NTSC rom image active, together with setting oscillator frequency). 2.) Even though you get standard PAL and NTSC by this method, PAL and NTSC have some ties with RF broadcasting standards, too. If you check a PAL and an NTSC motherboard, you find out that they also have different RF modulators. To keep the story short: the RF connection (using an RF cable between the computer and a TV's aerial outlet, and tuning in to a free channel) will most probably not work with the "newly implemented" video standard (ie. an NTSC machine in PAL and vice versa). Video signals (those found on the video port) are perfect, though...
|
