How how can I read serial data at a lower frequency than the device transmits it?

Question

I'm trying to get serial data from a device that I do not have control over. It is transmitting data at ~250 kHz, which is just too much for my Arduino/Raspberry to read and react to. This data is used on a device for a shift register, TPIC6C595

I want to be able to read this serial data at a lower clock. How can I achieve this?

The important thing is not only to read the data, but to read it with regard to the clear and latch signals that are coming into a register

A very basic idea is to make two cascades of shift registers, one cascade will read data at the device's clock and transfer it to parallel form and the other cascade will gather parallel data to serial at Arduino's clock. As I have 35 bits of info being stored, the wiring of this board will be real mess, andit seems overcomplicated.

I think I need something like a TPIC6C595, a shift register that reads serial data, stores it into storage register, but instead of parallel data output has a serial output on different clock. Is there such an IC?

Do you have any other ideas on how can I do it?

Answer 1

I understand that you want a microcontroller to pretend to be a 74xx595 shift register, so it receives the same data when connected in parallel with a real 74xx595 shift register.

250kHz is not that fast for data transmission, but possibly too fast for bit-banging on a slower microcontroller. See if your microcontroller has a feature called SPI slave, or USART. The signal you want can be received by either of these. The hardware will gather the bits into bytes and then you only have to read the bytes, so the microcontroller is fast enough.

Or, get a faster microcontroller. There are many that are fast enough to bit-bang 250kHz.

Answer 2

If you insist on buffering data, a FIFO such as 74ACT2229 might be usable. You will need additional logic to track state of the buffer and read it out, or perhaps use a wider (e.g. 64x4 or more) one if you want to record more status lines at the same time, or even make something more akin to a logic analyzer. (Which won't be any easier to read out via MCU, and will most likely need an FPGA to build practically.)

You'll notice this device is rather obscure, expensive and poorly stocked. Likely the reason is this type of device is largely obsoleted by the availability of fast MCUs, with good peripherals, and FPGAs. This is why other comments have urged a solution using such resources. Perhaps it's not a perfect fit for whatever data you're trying to read, perhaps it can be made to work with a little cleverness.