CAN ISO-TP Utility

ISO-TP CAN Frame Calculator

Split diagnostic or application payloads into ISO-TP CAN frames, calculate Single Frame, First Frame and Consecutive Frame PCI bytes, inspect sequence numbers and estimate separation timing. You can also decode an individual ISO-TP CAN frame including Flow Control parameters.

✓ ISO 15765-2 ✓ Single Frame ✓ First Frame ✓ Consecutive Frames ✓ Flow Control

ISO-TP Frame Calculator

● Ready

Operation Encode mode segments a payload. Decode mode inspects the PCI and data of one CAN frame.

CAN Data Capacity This calculator uses the conventional 8-byte ISO-TP CAN frame layout.

Payload / ISO-TP Frame Hex Bytes Hex bytes may use spaces, commas, colons, hyphens or 0x prefixes. Encode mode accepts up to 4095 payload bytes in this classic 12-bit length model.

Flow Control Block Size 0 means the sender may continue without waiting for another Flow Control frame.

STmin Byte 0x00–0x7F represent 0–127 ms. 0xF1–0xF9 represent 100–900 µs.

Pad generated CAN frames to 8 bytes

Padding Byte Used only when frame padding is enabled.

ISO-TP model: this calculator implements the conventional ISO 15765-2 PCI layout for Classical CAN. A Single Frame carries up to 7 payload bytes. A multi-frame transfer starts with a First Frame carrying 6 payload bytes, followed by Consecutive Frames carrying up to 7 payload bytes each.

ISO-TP CAN Result Calculated

ISO-TP Result —

Payload Length —

Transfer Type —

Total Frames —

First Frame Data —

CF Data Capacity —

Consecutive Frames —

Block Size —

STmin —

Sequence Start —

Padding —

Minimum CF Gap Total —

PCI —

#	Frame Type	Sequence	PCI	Payload	CAN Data Bytes

Calculation Breakdown —

What Is ISO-TP on CAN?

ISO-TP, commonly associated with ISO 15765-2, is a transport protocol used to carry messages that may be larger than the payload of a single CAN data frame. It is widely encountered in automotive diagnostics and other CAN-based systems.

ISO-TP adds Protocol Control Information, or PCI, to the CAN data field so the receiver can determine whether a message is a Single Frame or part of a multi-frame transfer.

ISO-TP Frame Types

PCI Type	High Nibble	Purpose
Single Frame	0x0	Complete short message
First Frame	0x1	Starts a multi-frame message
Consecutive Frame	0x2	Continues payload data
Flow Control	0x3	Controls sender pacing

ISO-TP Single Frame

With the conventional Classical CAN layout, the first data byte contains the Single Frame PCI and payload length. This leaves seven bytes for application data.

Payload:
22 F1 90

Payload Length:
3 bytes

PCI:
03

CAN Data:
03 22 F1 90 00 00 00 00

ISO-TP First Frame

When the payload is longer than the Single Frame capacity, the transfer begins with a First Frame. The conventional First Frame uses two PCI bytes and carries the first six payload bytes.

Payload Length:
17 decimal
= 0x011

First Frame PCI:
10 11

First Frame:
10 11 [first 6 payload bytes]

ISO-TP Consecutive Frames

After the First Frame and appropriate Flow Control, the remaining data is sent using Consecutive Frames. The first byte is the PCI and the remaining seven bytes can contain payload data.

Consecutive Frame PCI:

21 = Sequence 1
22 = Sequence 2
23 = Sequence 3
...
2F = Sequence 15
20 = Sequence 0

Sequence numbers wrap modulo 16.

How Many ISO-TP Frames Are Required?

For Classical CAN:

If payload ≤ 7 bytes:
Total Frames = 1

If payload > 7 bytes:

First Frame carries 6 bytes.

Remaining =
Payload Length - 6

Consecutive Frames =
ceil(Remaining / 7)

Total Frames =
1 + Consecutive Frames

ISO-TP Flow Control Frame

A Flow Control frame tells the sender whether it may continue transmitting and provides pacing parameters such as Block Size and STmin.

Example:
30 00 05

30 = Flow Control / Continue To Send
00 = Block Size 0
05 = STmin 5 ms

Flow Status Values

FS	Meaning
0	Continue To Send (CTS)
1	Wait
2	Overflow / Abort

ISO-TP Block Size

Block Size defines how many Consecutive Frames the sender may transmit before it must wait for another Flow Control frame. A Block Size of zero allows the remaining Consecutive Frames to be sent without another block boundary imposed by that Flow Control message.

ISO-TP STmin

STmin specifies the minimum separation time requested between Consecutive Frames. Values from 0x00 through 0x7F represent milliseconds. The encoded values 0xF1 through 0xF9 represent 100 through 900 microseconds.

0x00 = 0 ms
0x05 = 5 ms
0x7F = 127 ms

0xF1 = 100 µs
0xF5 = 500 µs
0xF9 = 900 µs

ISO-TP Sequence Number

Each Consecutive Frame contains a four-bit Sequence Number. The first CF after the First Frame normally uses sequence number 1. The value increments for each following CF and wraps after 15 back to 0.

CF sequence:

1, 2, 3, ... 14, 15, 0, 1, 2 ...

Example: 20-Byte ISO-TP Payload

Payload:
20 bytes

First Frame Payload:
6 bytes

Remaining:
20 - 6 = 14 bytes

CF Capacity:
7 bytes

Consecutive Frames:
14 / 7 = 2

Total:
1 First Frame + 2 CF
= 3 CAN frames

ISO-TP CAN Frame Calculator FAQs

What does ISO-TP mean?

ISO-TP is commonly used as shorthand for the ISO 15765-2 transport protocol used to transfer larger messages over CAN.

How much data fits in a Classical CAN ISO-TP Single Frame?

With the conventional one-byte Single Frame PCI layout used by this calculator, up to seven application-data bytes fit in an eight-byte CAN data field.

How much payload fits in the First Frame?

The conventional 12-bit First Frame length layout uses two PCI bytes, leaving six bytes for payload in an eight-byte Classical CAN frame.

How much data fits in each Consecutive Frame?

A Consecutive Frame uses one PCI byte, leaving up to seven payload bytes.

What does ISO-TP sequence number 0 mean?

Sequence numbers use four bits and wrap modulo 16. After sequence 15, the next Consecutive Frame uses sequence 0.

What does Block Size 0 mean?

It means no additional Flow Control frame is required solely because a fixed number of Consecutive Frames has been reached.

What does STmin 0x05 mean?

It represents a requested minimum separation time of 5 milliseconds.

What does STmin 0xF5 mean?

It represents 500 microseconds.

Does this calculator include CAN arbitration and bus transmission time?

No. The displayed STmin timing is a transport-layer separation estimate. Actual elapsed time also depends on CAN arbitration, frame transmission, Flow Control traffic, processing delays and implementation behavior.

Does ISO-TP use CAN IDs?

Yes, ISO-TP communication is carried in CAN frames, but CAN identifier and addressing configuration are separate from the payload segmentation performed by this calculator.

Calculate ISO-TP CAN Message Segmentation

Split payload bytes into ISO-TP Single, First and Consecutive Frames, inspect PCI values and sequence numbers, or decode an individual transport frame and its Flow Control parameters.