Casio CDP-220R - Manual (Page 28)

19.3.15 Single Parameter Data Size Limit
With the Instrument’s system exclusive message format, the size of a single message cannot exceed 256
bytes. The data size and the array size, however, can cause a packet to exceed 256 bytes when transferring
a single parameter array. In this case, the IPS and IPR message data length and data index number
values can be modified to enable division of a single parameter value into multiple messages so it can be
sent that way.
19.3.16 img : Parameter Set Image
Format: LSB 0dddddddB
0cccccccB
MSB 000000abB
For a bulk data transfer operation, the parameter set data to be transferred is read sequentially in
16-bit units starting from the top address. Read values are divided into 3-byte segments as shown below,
and then sent in sequence.
The following is the conversion format, which is the same as the individual parameter 16-bit transfer
detailed above.
16-bit Memory Image
MSB: abccccccB
LSB: cdddddddB
↓
data0: 0dddddddB
data1: 0cccccccB
data2: 000000abB
If the length of the data begin transferred is an odd number of bytes, the final bit field is filled in
with zero.
Parameter Set Packet Division The maximum image size of the parameter set that can be sent
with one packet is 128 bytes. When data that exceeds 128 bytes is transferred, data is always divided
into 128-byte units, except for the final packet. Because of this, the data in received packets can be
stored in an areas the size of [P arameterSetStartAddress] + [P acketN umber]
× 128.
For bulk parameter set transfer, the 16-bit image is divided in 3-byte groups, so the img field length
is the value produced by multiplying the len value (len + 1 when len is an odd number) by 3/2. Note,
however, that a parameter set of 128 bytes or less can be sent using a single packet, and anything greater
than 128 bytes is divided among multiple packets. This means that the maximum length “data” field is
128
× 3/2 = 192 bytes.
Only one parameter set can be transferred per session, and data from different parameter sets cannot
be mixed within a single packet, even when sending multiple parameter sets. Different parameter sets
are always divided into separate packets.
19.3.17 sum : Check Sum
Format: 0sssssssB
In this case, this “sum” field contains a value, which, when added to the total value of the “img”
field, makes the lower seven bits 0. The receiving side checks if this is true, and performs error handling
(re-request, etc.) if it is not.
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