ISDU buffering is intendent to increase reading/writing ISDU, using internal ISDU cache, where requested ISDU will be queued To increase processing ISDU, each response can consists ISDU responses(s). The maximum summury of ISDU responses is limited to 250 bytes for each response packet.

The structure of ISDU request:
[Packet length : 1 byte] : [CRC:1] : [Command 0x30 : 1] : [ISDU : max 232 bytes]
[ISDU Structure]
[Transaction ID : 1 byte] - used to create relation between request and response
if < 128 - normal request
if > 128 - no request data, only check if response is available
[Index : 2 bytes]
[Subindex: 1 bytes]
[ISDU length: 1 bytes] - for read request should be 0
[ISDU Write Data: 1..232 bytes] - ISDU data for write request

The structure of ISDU response:
[Packet length : 1 byte] : [CRC:1] : [Request result : 1] : [ISDU responses : max 250 bytes]
[Request result] this byte consist result of requested data:
0 - previous request was stored in Master and will be processed
1-2 - previous request was NOT stored because of full buffers, the previous request should be repeated
3-255 request error. The request is incorrector internal error
[ISDU responses : max 250 bytes]
[ISDU - 0]
[Transaction ID : 1 byte] 0-6 bits transaction ID, bit 7, if 1 shows an ISDU error
[ISDU response length: 1 byte] : up to 232 bytes for read, 0 for write, 2 bytes for ISDU error
[ISDU data : 0 - 232 bytes] - for read and error responses
[ISDU - 1]
[Transaction ID : 1 byte] 0-6 bits transaction ID, bit 7, if 1 shows an ISDU error
[ISDU response length: 1 byte] : up to 232 bytes for read, 0 for write, 2 bytes for ISDU error
[ISDU data : 0 - 232 bytes] - for read and error responses
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