83Redux: Part Two – Fujitsu 29LV400TC (U15)


Uncovering the Part Number

The examined main board of the TI83 Plus (Rev A) graphing calculator uses a Fujitsu 29LV400TC-90PFTN flash memory module. This module provides up to 512kb of memory and can operate in either 8-bit or 16-bit mode. The board uses the module in 8-bit mode, which provides 524,288 bytes of memory.

The print on the chip was a little difficult to make out, with the paintpen markings on it, so I used image editing software to better see the markings.

The flash module appears to be branded Fujitsu, but this module also appears on the market branded as AMD and Macronix. Macronix is one of the world’s largest solid state memory manufacturers. It is believed that the Fujitsu module on the provided board was superseded by the Macronix MX29LV400C.

In this application, the flash module is used in ‘BYTE’ mode, meaning that several of the data output pins are not used and not connected. These pins are 30, 32, 34, 36, 39, 41, and 43 and are left floating.

Interesting Supply Chain Workaround

The datasheet of this flash module lists that Pin 16 should not be connected (N.C.), but the board being examined has a connection on this pin. It is believed that this connection, from Pin 16 of the flash module to U11 Pin 41, allows the assembler to use either the 29LV400 flash module or the larger 29LV800 flash module. This is made possible because the 29LV800 flash module uses Pin 16 as the most significant bit of the memory address, which would also double the memory addresses available, but it would still only operate in BYTE mode.

U15 – Original Hardware (Circa 2003)
U15 – Redesigned in CAD Software
Original on Left | Redesigned by Cyber City Circuits on Right.

Fujitsu 29LV400TC-90PFTN Derived Pinout

Pin on Flash ModuleFujitsu 29LV400TC-90PFTN
(U15) Datasheet Reference
Connection to Inventec
Controller (U11)
1A15U11 – 48
2A14U11 – 49
3A13U11 – 51
4A12U11 – 52
5A11U11 – 54
6A10U11 – 56
7A09U11 – 57
8A08U11 – 58
9No ConnectNo Connect
10No ConnectNo Connect
11~WEU11 – 22
12~RESETU11 – 35
13No ConnectNo Connect
14No ConnectNo Connect
15Ready/~BusyNo Connect
16NC – Used with 29LV800 ModuleU11 – 41
17A17U11 – 46
18A07U11 – 59
19A06U11 – 60
20A05U11 – 61
21A04U11 – 62
22A03U11 – 63
23A02U11 – 64
24A01U11 – 67
25A00U11 – 68
26~CEU11 – 31
28~OEU11 – 21
29DQ00U11 – 79
30DQ08No Connect
31DQ01U11 – 76
32DQ09No Connect
33DQ02U11 – 75
34DQ10No Connect
35DQ03U11 – 74
36DQ11No Connect
38DQ04U11 – 73
39DQ12No Connect
40DQ05U11 – 72
41DQ13No Connect
42DQ06U11 – 71
43DQ14No Connect
44DQ07U11 – 70
45DQ15U11 – 69
48A16U11 – 47
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