HP41 TULIP4041 update

[MeindertKuipers]

Thanks for the clarification Christoph! Learned something again.

Some have been playing with the TULIP already, and I wanted to share some of the design trade-offs.

FI input
The FI input is used only for tracing the FI line, and does not have any real function for the TULIP. The FI output of course is critical for the operation of some modules, including HP-IL. The final module version will not have the FI input because it requires an extra level shifter and there is simply not enough space on the module PCB. There will be an FI output of course. And based on this output you will still be able to see when the FI line is driven by the TULIP, but you cannot see any FI activities from outside the TULIP (like TIME on the 41CX). If you still wish to trace FI, than simply use the TULIP DevBoard.
The FI input has a jumper. This can be used to isolate FI and and expose GPIO2. This can then be used as an SPI or I2C port to connect a display, RTC or other goodies with your own TULIP firmware version
IR out and PWO outputs
The TULIP uses almost all available GPIOs, and the Pico2 module does not expose all RP2350 GPIO's. Therefore the IR and PWO outputs are shared, and also jumpered to expose GPIO3 to able able to offer SPI or I2C together with GPIO2.
The TULIP module version will have its own independent IR and PWO outputs, with a solder jumper on PWO for just an extra spare GPIO.
UART on GPIO0 and GPIO1
This is a remnant from the first development cycle, and it is still used by me to experiment in situations where a USB connection is not desired (power mode testing). I normally connect this to the UART on the Pico Probe. This UART will be available on the module version. As a possible use it is foreseen to be connected with the new PILBox to have a real HP-IL loop interface.
TULIP Power
On the DevBoard there is a FET to allow power switching between USB power and HP41 power. The FET is there to allow the TULIP to be powered from USB even when HP41 power (which has a higher voltage) is present to prevent draining the HP41's battery. It is not intended to power the HP41 from USB. There is a jumper on the HP41 VBAT line to prevent the TULIP to be powered from the calculator when there is no USB connection, this is your choice. On the final module this will be a solder jumper, which is bridged by default. Cut the trace if you do not want this.
And I still have to do tests on the low-power modes of the RP2350.
TULIP module version
I have a draft schematic and layout of the module. The main differences with the DevBoard are:
- maximum amount of FLASH, 16 MByte, hand solderable SOIC-8 footprint
- USB-C connector, micro SD card holder
- no FI input, only FI output tracing
- an RTC is foreseen for TIME emulation,. This requires an external battery and adapted housing
- IR led, on-board LED (considering multi-colour) and PWO driving
- connections (for 2mm header) with I2C/UART/debug/BOOT/RUN/spare. I2C shared with RTC
- 3D printed housing

Always happy to get feedback. In a next post I will point out some of the plans I have with the firmware and functionality.