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TC0650 FDA
“F3 Digital to Analog”

The fda handles color blending and output. for each screen pixel, it reads two rgb colors from color ram (whose address is controlled by the fdp) and some blending info from the fdp (a 4-bit alpha value and a few more bits to control blur, palette mode, additive blending, etc.). it then blends these colors and outputs the result as analog rgb.

The fda also allows the cpu to read and write color ram, with help from the fdp. (i assume it just connects the cpu data bus to color ram data, when instructed to by the fdp or fcm)

Pinout

1	nc
2	i	? GND
3	i	alpha0	Fdp
4	i	alpha1
5	i	alpha2
6	i	alpha3
7	i	blur
8	io	D16	Cpu Data (16-bit)
9	io	D17
10	io	D18
11	io	D19
12	io	D20
13	io	D21
14	io	D22
15	VCC
16	GND
17	io	D23
18	io	D24
19	io	D25
20	io	D26
21	io	D27
22	io	D28
23	io	D29
24	io	D30
25	io	D31
26	i	fcm.99?
27	i	fcm.97?
28	i	fcm.98?
29	i	cpu R/W
30	nc

31	GND
32	VCC
33		VREF 0.35V	Blue Dac
34		VREF 5V
35		AGND
36		AVCC
37	o	color output
38	nc
39	o	color output	Green Dac
40		AVCC
41		AGND
42		VREF 5V
43		VREF 0.35V
44	o	color output	Red Dac
45		AVCC
46		AGND
47		VREF 5V
48		VREF 0.35V
49	GND
50	VCC

51	nc
52	nc
53	io	D7	Color Ram 1 Data
54	io	D6?
55	io	D5?
56	io	D4?
57	io	D3?
58	io	D2?
59	io	D1?
60	io	D0?
61	io	D7?	Color Ram 2 Data
62	io	D6?
63	io	D5?
64	io	D4?
65	GND
66	VCC
67	io	D3?
68	io	D2?
69	io	D1?
70	io	D0?
71	io	D7?	Color Ram 3 Data
72	io	D6?
73	io	D5?
74	io	D4?
75	io	D3?
76	io	D2?
77	io	D1?
78	io	D0?
79	nc
80	nc

81	VCC
82	GND
83	o	? unused
84	o	? unused
85	o	color ram output enable
86	o	color ram 3 write enable
87	o	color ram 2 write enable
88	o	color ram 1 write enable
89	i	RESET
90	GND
91	VCC
92	i	half-pixel clock (13.343 MHz)
93	i	inverted pixel clock (6.6715 MHz) (jp2)
94	i	? VCC
95	i	mode0	Fdp
96	i	mode1	Fdp
97	i	? GND
98	i	fdp.181 (cpu?)
99	VCC
100	GND

I don't remember which byte of the color is stored in which color ram chip. Here i've labelled them "1" (IC38), "2" (IC39), "3" (IC40).

TC0650 FDA“F3 Digital to Analog”

Pinout

TC0650 FDA
“F3 Digital to Analog”