Cassette
The FRED 1 and 1.5 prototypes are not using the 1802 EF and Q flags for tape I/O like most of the CDP1802 machines. Instead dedicated tape HW was build to handle the tape I/O, including logic to start the tape and to detect if the tape is running.
I expect the first FRED 1 prototype included HW to support the '5.2/6.2 Tone' format. This format uses tones with different frequencies to identify '1' or '0' values. 5.2 KHz tones represent a '0' and 6.2 KHz tones represent a '1'. Every tone is 5 ms and is followed by a silence of 5 ms.
In February/March 1973 the FRED tape format was changed to the 'PM (Pulse Mode) System'. This format was introduced due to the fact that the 5.2/6.2 Tone format was rather slow and not reliable enough. The PM System uses 3.3 KHz tones and identifies '1' or '0' values based on number of cycles (or pulses). A '1' is represented as 5 cycles of the 3.3 KHz tone followed by a 1.2 ms silence and a '0' is represented as 2 pulses.