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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 palette RAM (whose address is controlled by the FDP) and some blending info from the FDP (likely 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 palette RAM, with help from the FDP. (i assume it just connects the CPU data bus to palette RAM data, when instructed to by the FDP or FCM)

Pinout

1	nc??
2	GND
3	fdp.196
4	fdp.197
5	fdp.198
6	fdp.199
7	fdp.202
8	D16	CPU data (16-bit)
9	D17
10	D18
11	D19
12	D20
13	D21
14	D22
15	VCC
16	GND
17	D23	CPU data (16-bit)
18	D24
19	D25
20	D26
21	D27
22	D28
23	D29
24	D30
25	D31
26	fcm.99?
27	fcm.97?
28	fcm.98?
29	CPU R/W
30	?

31	GND
32	VCC
33	VREF 0.35V	Blue
34	pullup R15
35	GND
36	VCC
37	blue output
38	nc?
39	green output	Green
40	VCC
41	GND
42	pullup R15
43	VREF 0.35V
44	red output	Red
45	VCC
46	GND
47	pullup R15
48	VREF 0.35V
49	GND
50	VCC

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

81	VCC
82	GND
83	?
84	?
85	palette RAM output enable
86	palette RAM 3 write enable
87	palette RAM 2 write enable
88	palette RAM 1 write enable
89	CPU reset
90	GND
91	VCC
92	13.343 MHz clock
93	inverted 6.6715 MHz clock (through jp2)
94	VCC
95	fdp.203
96	fdp.204
97	GND
98	fdp.181
99	VCC
100	GND

i don't remember which byte of the color is stored in which palette 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”