NTSC Spectrum

One example of an NTSC Spectrum (as opposed to a Timex machine) has been found (in Chile). As far as is known, it is the same as a normal (PAL) Spectrum with the following differences:


 * The CPU is clocked at 3.5275 MHz
 * One frame lasts 0xe700 (59136) tstates, giving a frame rate of 3.5275×106 / 59136 = 59.65 Hz
 * 224 tstates per line implies 264 lines per frame.
 * The first contended cycle is at 0x22ff (8959). This implies 40 lines of upper border, 192 lines of picture and 32 lines of lower border/retrace.
 * The contention pattern is confirmed as being the same 6,5,4,3,2,1,0,0 as on the 48K machine.

Many thanks to Claudio Bernet for running all the tests on his machine.