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PassThruQueueMsgs v5.0

Queue messages on a channel for transmission

Last updated: January 13, 2026

Description

The function places messages into the transmit queue of the pass-thru device for the specified channel. On success, STATUS_NOERROR is returned, and the value pointed to by pNumMsgs is updated to contain the actual number of messages that were queued.

long PassThruQueueMsgs(
    unsigned long ChannelID,
    PASSTHRU_MSG *pMsg,
    unsigned long *pNumMsgs
)

Operational details

• Messages are placed into the queue in the order in which they are passed in (the message at index 0 is first, at index 1 is second, and so on)
• A message must fit into the transmit queue in its entirety
• The function does not wait for space to become available in the queue
• The structures pointed to by pMsg are not modified
• Messages submitted through this function have a lower priority than periodic messages (PassThruStartPeriodicMsg)

Specifics for ISO 15765 logical channels

ISO 15765 logical channels may queue a single frame whose network address or TxFlags do not match the RemoteAddress or RemoteTxFlags specified when the channel was created.

Parameters

ChannelID

Input parameter. The identifier of the physical or logical communication channel obtained from a call to PassThruConnect() or PassThruLogicalConnect().

pMsg

Input parameter. A pointer to an application-allocated array of PASSTHRU_MSG structures containing the messages to queue.

pNumMsgs

Input/output parameter. A pointer to an unsigned long variable:

• On call: contains the number of messages to queue
• On return: contains the actual number of messages that were successfully queued

Return error codes

Code	Description
STATUS_NOERROR	Function completed successfully. All messages were queued.
ERR_CONCURRENT_API_CALL	A J2534 API function was called before the previous call completed
ERR_DEVICE_NOT_OPEN	PassThruOpen() has not been successfully called
ERR_INVALID_CHANNEL_ID	Invalid ChannelID value
ERR_DEVICE_NOT_CONNECTED	Communication error with the pass-thru device. The device has been disconnected.
ERR_NOT_SUPPORTED	The device does not support this function for the given ChannelID
ERR_NULL_PARAMETER	pMsg or pNumMsgs is NULL
ERR_MSG_PROTOCOL_ID	The ProtocolID in the PASSTHRU_MSG structure does not match the channel's ProtocolID
ERR_INVALID_MSG	The message structure is invalid for the given ChannelID
ERR_MSG_NOT_ALLOWED	Attempt to queue a segmented message whose address/flags do not match the parameters of the ISO 15765 logical channel
ERR_BUFFER_FULL	The transmit queue is full. pNumMsgs contains the number of messages that were actually queued.
ERR_FAILED	Undefined error. Use PassThruGetLastError() to get a description.

Examples

C/C++ example

#include "j2534_dll.hpp"

unsigned long channelID = ...; // Channel ID from PassThruConnect/PassThruLogicalConnect

// Prepare the message
PASSTHRU_MSG msg = {0};
msg.ProtocolID = ISO15765;
msg.TxFlags = ISO15765_FRAME_PAD;

// Data: UDS Read Data By Identifier request (0x22)
unsigned char data[] = {0x00, 0x00, 0x07, 0xDF, 0x22, 0xF1, 0x90};
memcpy(msg.Data, data, sizeof(data));
msg.DataSize = sizeof(data);

unsigned long numMsgs = 1;

// Queue the message
long ret = PassThruQueueMsgs(channelID, &msg, &numMsgs);

if (ret == STATUS_NOERROR) {
    printf("Messages queued: %lu\n", numMsgs);
} else if (ret == ERR_BUFFER_FULL) {
    printf("Queue is full, messages queued: %lu\n", numMsgs);
} else {
    char error[256];
    PassThruGetLastError(error);
    printf("Error: %s\n", error);
}

Python example (ctypes)

from ctypes import *

j2534 = cdll.LoadLibrary("libj2534_v05_00.dylib")

# PASSTHRU_MSG structure
class PASSTHRU_MSG(Structure):
    _fields_ = [
        ("ProtocolID", c_ulong),
        ("RxStatus", c_ulong),
        ("TxFlags", c_ulong),
        ("Timestamp", c_ulong),
        ("DataSize", c_ulong),
        ("ExtraDataIndex", c_ulong),
        ("Data", c_ubyte * 4128)
    ]

channel_id = c_ulong(...)  # Channel ID

# Prepare the message
msg = PASSTHRU_MSG()
msg.ProtocolID = 0x06  # ISO15765
msg.TxFlags = 0x40     # ISO15765_FRAME_PAD

# UDS Read Data By Identifier request
data = bytes([0x00, 0x00, 0x07, 0xDF, 0x22, 0xF1, 0x90])
for i, b in enumerate(data):
    msg.Data[i] = b
msg.DataSize = len(data)

num_msgs = c_ulong(1)

# Queue the message
ret = j2534.PassThruQueueMsgs(channel_id, byref(msg), byref(num_msgs))

if ret == 0:  # STATUS_NOERROR
    print(f"Messages queued: {num_msgs.value}")
elif ret == 0x11:  # ERR_BUFFER_FULL
    print(f"Queue is full, queued: {num_msgs.value}")
else:
    error = create_string_buffer(256)
    j2534.PassThruGetLastError(error)
    print(f"Error: {error.value.decode()}")

Comparison with PassThruWriteMsgs (v04.04)

Characteristic	PassThruWriteMsgs (v04.04)	PassThruQueueMsgs (v05.00)
Behavior	Blocking call with timeout	Non-blocking, immediate return
Timeout parameter	Yes	No
Logical channel support	No	Yes

Related functions

• PassThruReadMsgs() - Read messages from a channel
• PassThruStartPeriodicMsg() - Start a periodic message (higher priority)
• PassThruSelect() - Select channels for monitoring
• PassThruLogicalConnect() - Create a logical channel

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