[FRAM71] Pre-Production Batch

[Hans Brueggemann]

the red LED's purpose somehow went "out of control" during the development process of the firmware and became more and more a handy debugging tool for me. That's why I never fully documented its function in the manual.
1) when inserting the FRAM71 into the HP-71B and then applying power, the internal states of the module are undefined, which sometimes leads to the LED being ON. (all FW versions)
2) pressing [ON] on the calculator brings FRAM71 into a known state, so it will switch the LED off. This is a good sign, because FRAM71 has accepted and properly decoded a RESET command. (all FW versions. it’s indeed a command, not just a reset pin being toggled)
3) Once FRAM71 is fully operational, switching your HP-71B off and then on again will result in a very brief and dim flash of the LED to indicate that the configuration registers of the “chips” are readied to accept data from HP-71B’s memory configuration routine. (FW 51x only. note that your HP-71B does a full memory configuration exercise on each start-up)
4) The LED will stay on as long as you have the write-protect status removed from the SYSRAM area, even if the HP-71B is off. (all FW versions)
5) The LED will blink when transmitting data over FRAM71’s UART (all FW versions)

6) FRAM71 Diagnostics that you can perform to verify proper operation:

1. Basically, 2), 3) tell you that FRAM71 is properly inserted into the cardreader bay, and that all data lines can be interpreted. sounds banal, but I had 2 FRAM71 buyers who had never used the cardreader port, so the contact pins had accumulated some foreign matter which prevented FRAM71 from properly communicating with the HP-71B. at that time, FRAM71 firmware didn’t have this diagnostic feature, which led to a mild panic among all parties ;o) If you ever face this problem, use isopropyl (isopropanol) and a cotton swab to clean the contacts. _DO NOT_ use WD40 or denaturated alcohol.
2. With the shipped configuration, you can do a POKE and PEEK$ to address 0x30000. If PEEK$ result matches POKE, then you have verified functionality of the CMD-decoder, the bidirectional RAM-interface, the PC/DP counters, the ID-register multiplexer, the STR-phase-shifter, and the MMU.
3. The LED can be tested by installing / removing CN2:4 (read the fine manual)
   

hans