Casio CFX-9970G (aka CFX-9990GT or Graph 80 in France)

This is a beast of a machine, very powerful features at their time, and the hardware implementation is uncommon having four stacked pcb boards.


The top pcb board module is a 8Mbits PROM firmware module inserted into a slot in the processor mainboard like we see in professional laptop computers.
The processor board interconnects with the other two boards (keyboard and display) using soldered flat cables.
The flat cable connectors are adequate to resist several maintenance operations without breaking.  They don't do it like this anymore.


Selecting System from the Menu, it tells me that it has just 63443 Bytes free after a clear memory operation.

Running the the self test by pressing F6 + a b/c + AC/ON.
This calculator shows this model code: ZX936

This CFX-9970GT shows 4MBit Version 1 + 8MBit Version 2.
I guess one of these ROM chips holds the CAS code.

This CFX-9970GT shows 128KB in the RAM test.

Same forensics result as found on other cfx-9850GB Plus series, so the processor is probably the same HCD62121 model.

 Dismantling to have a look inside.

The 8 Mbit PROM module, using a NEC µPD23C8000XGX.
Datasheet available here
Also here.
It can be configure as 1M 8-bit words, or 512K 16-bit words.

Note the configuration jumpers (zero Ohm resistors) setup:
R402 - Open
R403 - Closed
R404 - Open
R405 - Closed

Probably it can be possible to configure the operating system firmware to enable above the factory default 64KByte of SRAM, by changing the above setup. More information needed here...

The IC's on the mainboard:

- LSI101: unidentified IC
- LSI102: NEC µPD23C4001E 4Mbit with 512K 8-bit words PROM. NEC catalog here. 
- LSI103: SANYO LC3564SM 64KByte SRAM. Datasheet here.
- LSI104:  unidentified IC
- LSI105: CASIO F3660-ZD - Can't find information
- LSI106: EPSON SRM20V100LLMX7 128KByte SRAM. Datasheet here.

Casio CFX-9850GB Plus WE (White Edition) released in 2002

General parts view.

Processor PCA and Keyboard/Display PCA.

Contrast preset potentiometer.

Processor PCA. Main components:
- Hitachi HCD62121 Processor as per Wikipedia (reference not visible as it is sealed & hidden)
-  BSI BS62LV1024-70 128KByte SRAM 70nS
- OKI MR27V802D 1MByte PROM 100nS
- MC74HC4066A CMOS Quad Analog Switch
- 4.3MHz xtal with embedded caps set

 

SRAM reconfiguration to 64KByte.
The CFX-9850GB Plus WE  has a SRAM factory set to 32KByte. However the SRAM chip has 128KByte capacity.
Public information at several places states that it is possible to "upgrade" the SRAM size by changing the RAM setup jumpers. I read about it here.

Factory set to 32KByte: R20 jumper out, R21 jumper in.

Enable 64KByte: R20 jumper in, R21 jumper out.

It took me two minutes to to switch the jumpers. It was that easy and it is working fine on my machine.
Other machines may experience issues if the SRAM chip is defective.
Therefore it is essential to run the self test a few times to validate the new SRAM size good operation.

Basically I have unsoldered the jumper from R21 and soldered at R22 position.
This jumper looks like a SMD resistor but it has a zero Ohm value.

Assembling the calculator.
 

The Reset push button membrane and key contact.

The PCA is fixed using a few screws. No snap in / latches / rivets are used here.
Really a pleasure to work with when maintenance is required.
 

Idle current consumption: 2.5mA from 4 x AAA battery cells (6VDC).
 

Reconfirming that the new 64KByte SRAM sizing is recognized.
61396 Bytes available to the user. 

Running again the self test by pressing F6 + a b/c + AC/ON.

This calculator shows this model code: GY357

Testing the 8Mbit PROM.
ROM version 1.0. Four byte checksum = 0642FEA8

Testing the new 64KByte SRAM configuration.
RAMaddress = F7FF

Write/Read pattern: AA (a basic h/w test using a 10101010 binary combination).

Color LCD by CASIO.
Changing the contrast changes the temperature of each color. To see the Orange, Blue and Green colors will require a specific contrast setting, despite being possible to adjust the three individual colors as well.

Forensics test.
Result: 9.00000000733343