WP-34s from HP-30B: FTDI Board alternative FLASHing Instructions

[jebem]

(01-05-2015 10:18 AM)logicmonkey Wrote:  FTDI RX <- 1KOHM <- CALCULATOR TX

what is the reason for this? the calculator is at 3V0 and can't overdrive the FTDI device which is at 3V3

The data lines will swing from +V to Zero when sending the encoded data bits.
The serial TTL interface depends on current flowing to transfer the encoded data bits.
So this is just a best practice commonly used in electronics and it acts as a current limiter.
And of course it is handy to use small value resistors instead of bare wires if you are using the proposed method of not using a dedicated POGO plug

I did it in this way until I feed up dealing with unstable wire connections and decided to build my own flash box serial cable, equipped with dedicated internal 3.3V power supply and press buttons switches for Reset and Erase.
http://www.hpmuseum.org/forum/thread-1083.html