Note 1. The piezo element in the 41CL is driven by the same voltage as in the 41C, and is the same size as the original but is not quite as loud. This applies to all board revisions.

Note 2. WARNING! Never attempt to use YFWR or YFERASE on a Flash address in the OS area, or outside of the valid Flash address range. Acceptable Flash addresses are from 0x008000-0x0FFFFF for V2 boards and 0x008000-0x1FFFFF for V3 and V4 boards. The Flash address is not fully decoded in hardware, which means that addresses outside of the normal range will wrap around into the valid range. The newest versions of 41CL Extra and Extreme Functions will do a range check to prevent the problem: YFNS-4E, YFNZ-4E, YFNP-1E and YFNX-2B.

Note 3. All versions of the 41CL Extra Functions prior to -4C have an issue where several hidden status bits are not preserved during Deep Sleep (when the calculator is off). Most users will never notice the effects of this, but the issue has been addressed in YFNZ-4C. At the same time, this version also preserves the state of the Turbo mode while the calculator is off. But YFNZ-4C (or YFNS-4C or YFNP-1C) must be active for this to work, so always make sure that some version of the 41CL Extra Functions is always loaded in the machine.

Note 4. In versions of the FPGA programming prior to 03/12/14 the two-key rollover function didn't work like it should. The original HP specification for the CPU shows a state machine in the keyboard scanner that works with software to implement 2-key rollover, but the timing of the state transitions is not specified. In the design I used an instruction time to time the state transitions. After one user complained, I set up a simulation to see what was going on. In the 2-key-down case the state machine squirts through one state in less than a machine cycle. Blanking the keyscan during this time fixes the problem. All boards shipped after 03/12/14 have this issue corrected. I am happy to update boards in the field; just send me an email to arrange this.

Note 5. The SERINI function does not set the baud rate to 1200, so you still need to execute BAUDxx to properly set the baud rate.

Note 6. Several images appear not to be listed by CAT 2. They do show up if you halt the CAT and single-step through it. The reason for this is that the CAT function will only list entries with names longer than eight characters. (This was a 41-CX "improvement".) The images in question contain only user-code programs, with names too short to be listed in the main CAT function. The mnemonics known to have this issue are: BSMS (at 0x0CA), ISEN (at 0x0C9), LNDL (at 0x0CD) and TEST (at 0x0CE).