This is a specification drafted before the implementation, so it could be inaccurate. It is now slowly transformed into actual documentation.
These are the sub-commands implemented for the new E0h message:
D - SD-card root directory
M[dnnnnnnnn.eee] - mount file nnnnnnnn.eee on drive d
Nnnnnnnnn.eee - create an image file nnnnnnnn.eee
P[dw] - write protect drive d; w=0 RW, w=1 RO
Strictly speaking the D and N command should be send to the unit, not the drive. But this would mean a destination should be defined for this.
The original intention was to format the message on the Arduino-side, so the Z80 assembly code could just copy that to the display. This idea is somewhat abandoned due to space constraints.
Each command has a CP/M program that executes it and displays the result. These program use the Epson BIOS extension CALLX. With some luck the PX-4 implementation can be adapted to the PX-8.
D[0] returns first four root directory entries D[n] returns four root directory entries starting with the 4*nth an entry name starting with 0E5h indicates there are no more entries.
The D command returns a text block of up to 128 bytes containing up to eight directory entries (name and size)
All image file names are in the 8.3 format, as the SD library presents them. Directories have a '/' appended to the file name, but could overwrite the last extension character.
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eeesss<LF>
nnnnnnnn.eee is the filename in 8.3 format, sss are the three lowest bytes of an int (as returned by the SD-library.) This allows eight files in a 128 byte text block. Nice thing is the PX8/4 screen is eight lines high too. The three int bytes are converted to a decimal value. The PX-4 application PFDIR4 pauses after each part, ENTER or SPACE fetch the next part. Any other key aborts the program.
M returns the currently mounted images per drive Mdnnnnnnnn.eee mounts the image nnnnnnnn.eee on drive d and returns the currently mounted images per drive
The M command always returns a text block of 64 bytes containing drive letters and image names
Dnnnnnnnn.eeepRp<LF>
Ennnnnnnn.eeepRp<LF>
Fnnnnnnnn.eeepRp<LF>
Gnnnnnnnn.eeepRp<LF>
D, E, F, G are drives, nnnnnnnn.eee is the filename in 8.3 format, p is the Write-protect flag; 0 = RW, 1 = R0 R is a constant.
Nnnnnnnnn.eee creates an image named nnnnnnnn.eee in the SD card root directory. The size is 327680 bytes and its contents is all 0E5h.
The N command always returns an one byte text block and a single byte return code.
P returns the write protect flag state for all drives. Pdw sets or clears the write protect flag w for drive d and returns the write protect flag state for all drives.
The P command always returns a text block of 16 bytes containing drive letters and write protect-status.
D p
E p
F p
G p
This command is superfluous, as the write protect state could be specified at mount time. But this isn't implemented yet. The write protect state is already part or the PFMNT4 response.