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Serial.md

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Megadesk can be controlled/queried using serial communications.

Connect serial to the following programming header pins:

  • MISO -> RX
  • SCK -> TX
  • GND -> GND

Serial communications can use either human readable ascii or slightly more compact raw bytes.

compilation flags

Megadesk needs to be recompiled and flashed first as the default image doesn't have the serial features.

Two #define flags control megadesk serial communications:

  1. SERIALCOMMS - enables basic raw serial communications. required with every other flag below.
  2. HUMANSERIAL - enables human-readable ascii where each numeric field is separated by a non-digit character
  3. SERIALECHO - echo back the interpreted command before acting on it
  4. SERIALERRORS - Report errors over serial - reports timeouts, bad motor reads, user errors...

Human/Ascii Serial

After the marker byte '<', there's the Command byte, then two fields of ascii integer digits.

Terminate each field with any non-digit character eg !,./ or a line-break.

Missing digits are interpreted as zeros so <L.. is valid and passes two 0s to the L command.

First field (position) can be any number up to a maximum of 65535, the second field (slot) has a maximum of 255.

  data start (first byte)
    char   meaning
  -----------------
    <      start Rx Marker

  command (second byte)
    cmd    meaning
  -----------------
    +      increase position by
    -      decrease position by
    =      set absolute position
    C      Report current position
    S      Save position to (UpButton) EEPROM
    s      Save position to Downbutton EEPROM
    L      Load (Upbutton) position from EEPROM and move
    l      load Downbutton position from EEPROM and move
    W      Write arbitrary data to EEPROM
    R      Read arbitrary data from EEPROM
    T      play tone

  position (1st digit field or third/fourth bytes. max 65535)
    cmd    meaning
  -----------------
    +-     relative to current position
    =SsW   absolute position
    T      tone frequency
    CRLl   (ignore)

  push_addr (2nd digit field or fifth byte. max 255)
    cmd    meaning
  -----------------
    SLlWwR EEPROM pushCount/slot
    T      tone duration/4 ms. (250 == 1s)
    +-=C   (ignore)

Raw serial

Without HUMANSERIAL, always transmit 5 raw bytes:

ascii '<', command ascii byte, raw-MSB-position, raw-LSB-position, raw-slot

The '<' is the sync byte and indicates the start of a new message. Command bytes, position and slot ranges and values are the same as for Human serial.

Examples

Human serial commands, when using HUMANSERIAL

line breaks can be used instead of the final '.'

<W3000,3.     # writes location 3 with position 3000.
<T3000,255.   # plays a 3000Hz tone for 1sec
<C0.0.        # reports current position
<+300..       # nudge desk up by 300
<=3000.       # move to absolute position 3000
<L,2.         # recall position from slot 2
<l,2.         # recall position from down-button slot 2
<R.0/         # read eeprom slot 0
<L,17.        # toggle feedback pips
<L,18.        # toggle 2 button mode
<L,15.        # reset megadesk

Megadesk Responses:

>W3000,3    # successful response writing to slot 3
>T3000,255  # successful tone-play.
>=1323,0    # response to <C.. current position
>=5805,0    # response to <+ <- <= current position
>L6914,2    # successful recall of slot 2, target position of 6914 + beep and move
>R5715,2    # reports content of slot 2.

Megadesk error Responses (if SERIALERRORS is #defined):

>E0,1       # slot 1 is invalid slot for recall
>E0,33      # slot 33 is empty + sad trombone
>E6914,0    # error. requested position 6914 may be beyond min/max limits
Ec0,0       # invalid command 'c' (sent <c)
E<0,0       # too many txMarkers (sent <<)
DE2361,117  # legs reported positions differ by 117
8E2361,0    # communications problem with pid(leg) 8
!E57496,25  # 25ms delay was late by 7456us

esphome configuration

esphome example configuration avalible at esphome.md