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 It is believed that the Fujitsu module on the provided board was superseded by the Macronix MX29LV400C.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.
Fujitsu 29LV400TC-90PFTN Derived Pinout
| Pin on Flash Module | Fujitsu 29LV400TC-90PFTN (U15) Datasheet Reference | Connection to Inventec Controller (U11) |
|---|---|---|
| 1 | A15 | U11 – 48 |
| 2 | A14 | U11 – 49 |
| 3 | A13 | U11 – 51 |
| 4 | A12 | U11 – 52 |
| 5 | A11 | U11 – 54 |
| 6 | A10 | U11 – 56 |
| 7 | A09 | U11 – 57 |
| 8 | A08 | U11 – 58 |
| 9 | No Connect | No Connect |
| 10 | No Connect | No Connect |
| 11 | ~WE | U11 – 22 |
| 12 | ~RESET | U11 – 35 |
| 13 | No Connect | No Connect |
| 14 | No Connect | No Connect |
| 15 | Ready/~Busy | No Connect |
| 16 | NC – Used with 29LV800 Module | U11 – 41 |
| 17 | A17 | U11 – 46 |
| 18 | A07 | U11 – 59 |
| 19 | A06 | U11 – 60 |
| 20 | A05 | U11 – 61 |
| 21 | A04 | U11 – 62 |
| 22 | A03 | U11 – 63 |
| 23 | A02 | U11 – 64 |
| 24 | A01 | U11 – 67 |
| 25 | A00 | U11 – 68 |
| 26 | ~CE | U11 – 31 |
| 27 | VSS | GND |
| 28 | ~OE | U11 – 21 |
| 29 | DQ00 | U11 – 79 |
| 30 | DQ08 | No Connect |
| 31 | DQ01 | U11 – 76 |
| 32 | DQ09 | No Connect |
| 33 | DQ02 | U11 – 75 |
| 34 | DQ10 | No Connect |
| 35 | DQ03 | U11 – 74 |
| 36 | DQ11 | No Connect |
| 37 | VCC 3V | VCC 3V |
| 38 | DQ04 | U11 – 73 |
| 39 | DQ12 | No Connect |
| 40 | DQ05 | U11 – 72 |
| 41 | DQ13 | No Connect |
| 42 | DQ06 | U11 – 71 |
| 43 | DQ14 | No Connect |
| 44 | DQ07 | U11 – 70 |
| 45 | DQ15 | U11 – 69 |
| 46 | VSS | GND |
| 47 | ~BYTE | GND |
| 48 | A16 | U11 – 47 |