DATAMATH  CALCULATOR  MUSEUM

TI-88 Versions

Collecting electronic calculators, you'll sooner or later understand the importance of the TI-88 - the holy grail for Texas Instruments aficionados. We learned with the Phoenix Project the Five Engineering Stages and applied them to the ten different TI-88's we discovered so far. Digging deeper into the mechanical and electrical engineering of this calculator, we can define a total of five different versions:

TI-88 DVT (Design Validation Test)
TI-88 EVT (Engineering Validation Test)
TI-88 PVT 1 (Production Validation Test 1)
TI-88 PVT 2 (Production Validation Test 2)
TI-88 PVT 3 (Production Validation Test 3)

The differentiation between the three Engineering Stages DVT, EVT, and PVT is pretty straight forward with just glancing at the keyboard:

[ALPH] Key [R/S] Key Build: Notes
Design Validation Test Grey [ALPH] key
No dot next to [R/S] key
Engineering Validation Test Red [ALPH] key
No dot next to [R/S] key
Production Validation Test Red [ALPH] key
Red dot next to [R/S] key

We could analyze in the past years a total of five and a half TI-88 calculators and were looking into their Serial Numbers, Manufacturing Dates of the calculator, Markings on the Printed Circuit Boards (PCB) and more. Speculating about the reasons behind the cancelation of this outstanding calculator, we were looking closely into Markings of the Main Integrated Circuits (Part Designation, Revision, Manufacturing Code, Style of Marking). With some of the most complex Integrated Circuits (ICs) going through Revision "K" and sporting not even a Manufacturing Date Code while an earlier Revision "H" of the very same IC had final production status, we might have identified the reason for killing the TI-88...

TI Programmable 88 Versions

Serial Number Build Date of Manufacture PCB Main ICs Timekeeping
Controller
Master
Controller
Arithmetic
Controller
RAM ROM Diode-Mod
9-26-81-43 DVT wk 39
year 1981
3500 2901
Revision -
No Date Code
Proto Package
2902
Revision -
No Date Code
Proto Package
Not visible
Piggy pack
531
Revision A
No Date Code
Proto Package
5402
Revision B
No Date Code
Proto Package
No
NTC-3-4-30-82 EVT wk 17
year 1982
7999 01 PP
Revision C
No Date Code
Proto Package
02 PP
Revision C
No Date Code
Proto Package
Not visible
Piggy pack
0531
Revision BL
No Date Code
Proto Package
CD5402
Revision C
No Date Code
Proto Package
No
000337 PVT 1 wk 21
year 1982
8000 01 PP
Revision C
No Date Code
Proto Package
02 PP
Revision C
No Date Code
Proto Package
Not visible
Piggy pack
0531
Revision BL
No Date Code
Proto Package
CD5402
Revision C
No Date Code
Proto Package
No
000341 PVT 1 wk 21
year 1982
8000 CD2901
Revision H P
wk 27 year 1982
Series Package
CD2902
Revision ? P
Not visible
Series Package
Not visible
Piggy pack
0531
Revision BL
No Date Code
Proto Package
CD5402
Revision C
No Date Code
Proto Package
No
001101 PVT 2 wk 32
year 1982
8449 CD2901
Revision ?
DC not visible
Series Package
CD2902
Revision H P
wk ?? year 1982
Series Package
Not visible
Piggy pack
TP531
Revision C
No Date Code
Proto Package
CD5402
Revision C P
wk 27 year 1982
Series Package
Yes
002023 PVT 3 wk 33
year 1982
8449 2901
Revision K
No Date Code
Proto Package
2902
Revision K
No Date Code
Proto Package
Not visible
Piggy pack
TP531
Revision C
No Date Code
Proto Package
CD5402
Revision E
wk 31 year 1982
Series Package
Yes

Diode-Modification

While analyzing the Printed Circuit Boards (PCB) of various TI-88 builds, we noticed with both the TI-88 PVT 2 (Serial Number 001101) and TI-88 PVT 3 (Serial Number 002023) a minor modification with two additional diodes near one of the battery contacts and the Peripheral I/O connector J2.

Reverse engineering the schematics of this modification we immediately understood:

Don't connect a CA-800 Cassette Interface or a PC-800 Printer to TI-88 calculators without the Diode-Modification!

The two additional diodes added to the Serial Input/Output (S I/O) pin at the Peripheral I/O Connector prevent the TP530 Integrated Circuits (ICs) inside the Plug-In CROM/CRAM Modules from a latch-up possible with the peripheral powered up and the TI-88 powered down.

 

 

horizontal rule

If you have additions to the above article please email: joerg@datamath.org.

Joerg Woerner, October 9, 2019. No reprints without written permission.