Function userVideoRom2K

source/NTSC_CharSet.cpp:183–235

static void userVideoRom2K(csbits_t csbits, const BYTE* pVideoRom, const eApple2Type type = A2TYPE_APPLE2, const int AN2=0);

static void userVideoRom2K(csbits_t csbits, const BYTE* pVideoRom, const eApple2Type type /*= A2TYPE_APPLE2*/, const int AN2/*=0*/)
{
	for (int i=0; i<256; i++)
	{
		int RA = i*8;	// rom address

		if (type == A2TYPE_APPLE2JPLUS)
		{
			// AN2=0: $00-3F, $00-3F; $80-BF, $80-BF => KKAA (Repeat Katakana)
			// AN2=1: $40-7F, $40-7F; $C0-FF, $C0-FF => AAAA (Repeat ASCII)
			RA &= ~(1<<(6+3));
			RA |= (AN2<<(6+3));	// AN2 controls A9 (UTAII 8-12, Fig 8.7)
		}

		for (int y=0; y<8; y++)
		{
			BYTE n = pVideoRom[RA+y];

			// UTAII:8-30 "Bit 7 of your EPROM fonts will control flashing in the lower 1024 bytes of the EPROM"
			// UTAII:8-31 "If you leave O7 (EPROM Output7) reset in these patterns, the resulting characters will be inversions..."
			// Apple II J-Plus: simplest logic is just invert if reading low 1K of video ROM
			// Base64A: Bit 0 instead of bit 7
			if (RA < 1024)
			{
				if (type == A2TYPE_BASE64A)
				{
					if (!(n & 0x01))
						n = n ^ 0xfe;
				}
				else
				{
					if (!(n & 0x80) || (type == A2TYPE_APPLE2JPLUS))
						n = n ^ 0x7f;
				}
			}

			BYTE d = 0;
			if (type == A2TYPE_BASE64A)
			{
				// On the Base 64A bits are ordered 1345672.
				d = (n >> 2) | ((n & 2) >> 1) | ((n & 4) << 4);
			}
			else
			{
				// UTAII:8-30 "TEXT ROM pattern is ... reversed"
				for (BYTE j = 0; j < 7; j++, n >>= 1)	// Just bits [0..6]
					d = (d << 1) | (n & 1);
			}

			csbits[0][i][y] = d;
		}
	}
}

static void userVideoRomForIIPlus(void)
{