Manual

3.b.4. Command 168: Store Note

Effect: This command is used to store a sequence of notes in the mega168’s EEPROM that can then be played

as a melody. Each stored note consists of an 8-bit note-frequency enumeration byte and a 16-bit millisecond-

duration word. For details on note enumeration, see the Play Note command (152—Section 3.b.1). Specifically,

this command adds the three bytes of note data to the end of the melody currently under construction, storing it

in EEPROM. After a hardware reset, the melody currently under construction is set to melody 0. It is possible to

store up to 8 melodies and up to 159 total notes. The notes can be distributed among the eight melodies in any

way. The “current melody” counter is incremented by the End Melody command (224—Section 3.b.5).

Storing melodies can be rather slow given that each EEPROM write takes ~3.4 ms and storing a note requires

three EEPROM writes. Typically, the code to store melodies will be executed once at the beginning of a program

and then removed from that program. It is crucial that you give enough time between successive issuances of these

commands for EEPROM to be written. If you simply stream these commands to the mega168, notes will be lost.

A safe delay between issuances would be 15 ms. At a minimum the delay should be 10.2 ms. Alternatively, you

can ensure EEPROM is ready for the next store-note command by polling with the “Check If EEPROM Busy”

command (254—Section 3.d.04), which returns zero if it’s ok to read from/write to EEPROM.

Values sent: note (8 bits), duration (16 bits)

command byte = 168 | (MSB data byte 3 << 2) | (MSB data byte 2 << 1) | MSB data byte 1

data byte 1 = 7 lower bits of note byte

data byte 2 = most significant byte of duration word (missing MSB)

data byte 3 = least significant byte of duration word (missing MSB)

3.b.5. Command 224: End Melody

Effect: Terminates the melody currently under construction by advancing the next melody’s pointer to point to

the location in EEPROM that would be the first note of the next melody. The “current melody” counter is then

incremented so the next Store Note command (168—Section 3.b.4) will store the first note of the next melody. It

is possible to store up to 8 melodies. The End Melody command performs two EEPROM writes and hence it is

recommended you allow it at least 6.8 ms before transmitting a command that will cause the mega168 to perform

an EEPROM write.

Values sent: none

Command byte = 224

3.b.6. Command 186: Erase Melodies

Effect: Resets the melody pointers to a state that represents zero stored melodies. It is not necessary to call this

function before storing a new set of melodies, but it can prevent you from having unwanted “garbage” melodies

left in EEPROM. One way to get a garbage melody would be to store eight melodies (0 – 7), perform a hardware

reset, and then store two melodies (0 and 1). The pointers for melodies 2 through 7 were not updated by the most

recent store commands, however the notes in EEPROM have changed. Attempting to play melody 2 could result

in some unexpected sequence of notes. This command will cause the mega168 to perform nine EEPROM writes,

so it is recommended you give it at least 30.6 ms before issuing another command that will cause the mega168 to

perform an EEPROM write.

Values sent: none

3. Low-Level SPI Commands Page 14 of 27