DM42: The internal view (hardware components)

[jebem]

Currently (2018, February), there is little information on the hardware platform besides the processor type and memory. The same applies to the firmware building components.

May-2019 update:
Q1 seems to be a 20ppm part, so a RTC built around it would result in several minutes time drift after one year.

From the point of engineering view, it is essential to know what is the hardware design in order to fully understand the calculator low level software components.

So far no one have published reverse engineering reports or just a brief analysis of the calculator internals.
In fact I couldn't even find any high resolution photos of the PCB to learn what components were included in the hardware design.

Recently I found this medium resolution picture, and it allowed to uncover some more details.
I understand that there are several hardware versions, and the PCB in the picture would be the most recent version to this date (2018-Feb), marked with "calcbase3b (c) SwissMicros GmbH 2017".

I am publishing here a copy of the picture in question.




So far, i could identify the following hardware components:

Integrated Circuits:
- IC1: MX25R6435F M2ILO - Serial NOR FLASH ROM, 64Mbit (8M x 8), 80MHZ, 8-SOP package.
- IC3: STM32L476 VGT6 - SoC Processor (V = 100/104 pins, G = 1Mbyte Flash, T = LQFP 100-pin, 6 = -40°C to 85°C).
- IC4: 6-pin, Identification not readable in the picture
- IC5: 6-pin, Identification not readable in the picture
- IC7:LD3985 - LDO VR Ultra low drop and low noise BiCMOS voltage regulator.

Active components:
- UD1: UL46 - ST USBLC6-4 SOT23-6L package, very low capacitance ESD protection.
- D1: Diode, Identification not readable in the picture
- D2: Diode, Identification not readable in the picture
- Q2: Transistor, Identification not readable in the picture

Passive Components:
- Q1: 32.768K-E - CRYSTAL 32.768kHz, ±20ppm, 6pF, 50kOhms, 4-SOJ package.
- (Not listing here the capacitors and resistors).

So:
The total count of visible IC's are 5.
The total count of visible active components are 4.

This drawing (not to scale) list the above components in the PCB:




And here is a few initial observations from the above:

- Q1: This is a high precision crystal and curiously was marked with a transistor label in the PCB silkscreen (it should be marked as X1 imho).

- UD1: The USB connector (JP1) I/O data lines connected to the Processor, are protected against external ESD or over-voltage by UD1, a fast high current low capacitance Diode/Zener based integrated circuit.
This is good engineering from SwissMicros and they didn't cut costs to do a proper design here.

- IC7: Michael's comments on the LDO 3Volt regulator helped to identify IC7 that is not readable in the published picture, but from the IC pinout configuration it was easy to guess what this IC is.
So IC7 will be used when the calculator is connected via USB port to a computer, to regulate the external USB 5Volt down to 3Volt used to power the calculator, disabling the use of the internal CR2032 battery cell.
This allows to run the Processor at 80MHz instead of the regular 24MHz when the calculator runs on the battery.

- IC1 and IC3: These two are the most obvious integrated circuits that everyone is talking about, but they are not alone. This is not a two IC's design.

- IC5 and L1: IC5 is not readable in the published picture. However, it is close to the LCD connector.
Assuming that the LCD in use is a LS027B7DH01 from Sharp Microelectronics (is it?. I can't find the post where I read this a while ago), then it requires a 5Volt supply line to operate.
As the internal battery cell supplies just 3Volt, a step-up converter is needed and the IC5 and L1 combination may be in use for this purpose.
IC5 could be a single opamp on a 6-pin package, like the MAX4401 is.
Although a more conventional charge pump IC and capacitor (no inductor required) could be used here.
Just guessing.

- IC4 and Q2: IC4 is not readable in the published picture. But its close proximity to the buzzer would make it an audio driver (again, a MAX4401) using Q2 transistor to connect to the buzzer.
Again, just guessing.

And what about the "missing" IC2 and IC6 integrated circuits?
I mean, we have IC1 and IC7, therefore IC2 and IC6 could also belong to this design.
Could it be that there are more components on the other side of the moon, I mean, the PCB?

Any corrections, or even better, additional information on the hardware design and high resolution pictures of both sides of the PCB, is very welcome!