The IBM 79F2661 is a custom chip that appears to have been built specifically for the Teradrive, though it did get reused in the IBM PS/55 5510-Z. This chip is responsible for bridging the 286 and 68K busses and also for managing the 512KiB additional firmware ROM.

Pinout

This is still a WIP

Pin	Signal
1	VD6
2	VD7
3	VD8
4	VD9
5	VD10
6	VD11
7	VD12
8	VD13
9	VD14
10	VD15
11
12	LDS
13	UDS
14	R/!W
15
16
17	AS
18
19	VA1
20	VA2
21	VA3
22	VA4
23
24	VA5
25	VA6
26	VA7
27	VA8
28	VA9
29	VA10
30	VA11
31
32	VA12
33	VA13
34	VA14
35	VA15
36	VA16
37	VA17
38	VA18
39	VA19
40	VA20
41	VA21
42	VA22
43	VA23
44	GND maybe?
45	M68K CLK
55	286 A23
54	286 A22
53	286 A21
54	286 A20
55	286 A19
56	286 A18
57	286 A17
58	286 A16
59	286 A15
60	286 A14
61	286 A13
62	286 A12
63	286 A11
65	286 A10
66	286 A9
67	286 A8
68	286 A7
69	286 A6
70	286 A5
71	286 A4
72	286 A3
73	286 A2
74	286 A1
76	286 A0
77
78
79
80
81	286 M/!IO (might be off by a pin or 2)
118	VD0
119	VD1
120	VD2
121	VD3
122	VD4
123	VD5
124