Chapter 2. API Reference
Table 10: Table 4 Description of the register info structure:
mb_param_info_t
Field Description
time_stampthe time stamp of the event when defined parameter is accessed
mb_offsetstart Modbus register accessed by master
type type of the Modbus register area being accessed (See the mb_event_group_t for more informa-
tion)
address memory address that corresponds to accessed register in defined area descriptor
size number of registers being accessed by master
Example to get event when holding or input registers accessed in the slave:
#define MB_READ_MASK (MB_EVENT_INPUT_REG_RD | MB_EVENT_HOLDING_REG_RD)
#define MB_WRITE_MASK (MB_EVENT_HOLDING_REG_WR)
#define MB_READ_WRITE_MASK (MB_READ_MASK | MB_WRITE_MASK)
#define MB_PAR_INFO_GET_TOUT (10 / portTICK_RATE_MS)
....
// The function blocks while waiting for register access
mb_event_group_t event = mbc_slave_check_event(MB_READ_WRITE_MASK);
// Get information about data accessed from master
ESP_ERROR_CHECK(mbc_slave_get_param_info(®_info, MB_PAR_INFO_GET_TOUT));
const char* rw_str = (event & MB_READ_MASK) ? "READ" : "WRITE";
// Filter events and process them accordingly
if (event & (MB_EVENT_HOLDING_REG_WR | MB_EVENT_HOLDING_REG_RD)) {
ESP_LOGI(TAG, "HOLDING %s (%u us), ADDR:%u, TYPE:%u, INST_ADDR:0x%.4x, SIZE:%u
,→",
rw_str,
(uint32_t)reg_info.time_stamp,
(uint32_t)reg_info.mb_offset,
(uint32_t)reg_info.type,
(uint32_t)reg_info.address,
(uint32_t)reg_info.size);
} else if (event & (MB_EVENT_INPUT_REG_RD)) {
ESP_LOGI(TAG, "INPUT %s (%u us), ADDR:%u, TYPE:%u, INST_ADDR:0x%.4x, SIZE:%u",
rw_str,
(uint32_t)reg_info.time_stamp,
(uint32_t)reg_info.mb_offset,
(uint32_t)reg_info.type,
(uint32_t)reg_info.address,
(uint32_t)reg_info.size);
}
Modbus Slave Teardown This function stops the Modbus communication stack, destroys the controller interface,
and frees all used active objects allocated for the slave.
mbc_slave_destroy()
ESP_ERROR_CHECK(mbc_slave_destroy());
Possible Communication Issues And Solutions
If the examples do not work as expected and slave and master boards are not able to communicate correctly, it is
possible to find the reason for errors. The most important errors are described in master example output and formatted
as below:
Espressif Systems 631
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