Spectrum Serial Server
                            ======================
                                 Brief Notes

The Serial Server runs on a BBC connected to a Spectrum via the serial ports. The
Spectrum sends commands to the BBC via the serial port, optionally followed by a
LOAD or SAVE command.

At the Spectrum end, at some point, open the serial port and attach it to a
channel, eg:

    OPEN#9,"b"

Commands are issued along the lines of, (in pseudocode):

    PRINT #9;CHR$(command)+filename$ :REM Send command
    INPUT #9;reply$                  :REM Get reply
    IF reply$<>"" THEN errnum=CODE(reply$):errstr$=reply$(2 TO)
    IF reply$="" THEN perform any extra actions

Supported commands are:
    C Catalog
    D Change Directory
    E Erase
    H Help
    I Info
    L Load
    M Make Directory
    R Rename
    S Save
    X Exit

(C)at, (H)elp and (I)nfo are replied to with strings of text to print, terminated
with a null string.

(L)oad is followed by LOAD *b

(S)ave is followed by SAVE *b

Examples:

Catalog, Help
-------------
PRINT #9;"C":INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
PRINT #9;"H":INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)

Info, Directory, Erase, MkDir
-----------------------------
PRINT #9;"I"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
PRINT #9;"D"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
PRINT #9;"E"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
PRINT #9;"M"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)

Rename
------
PRINT #9;"R"+o$+" "+n$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)

Load
----
xxxx PRINT #9;"L"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
yyyy IF a$="" THEN LOAD *b/LOAD *b CODE/etc

Save
----
xxxx PRINT #9;"S"+f$:INPUT #9;a$:IF a$<>"" THEN PRINT a$(2 TO)
yyyy IF a$="" THEN SAVE *b/SAVE *b CODE/etc:RETURN

The filename passed to Save can include file addresses in decimal, for example:

LET f$=fn$+" "+STR$load+" "+STR$exec+" "+STR$auto+" "+STR$type


See also http://mdfs.net/Info/Comp/Spectrum/ProgTips/device.htm
for packaged subroutines.