> For the complete documentation index, see [llms.txt](https://inacks.gitbook.io/is4310-wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://inacks.gitbook.io/is4310-wiki/datasheet/memory-description/holdx-registers.md).

# HOLDx Registers

> This page is not the authoritative source for design information. The official [IS4310 datasheet](https://www.inacks.com/is4310) published on [www.inacks.com](http://www.inacks.com) is the authoritative reference: always consult it for the latest information.

HOLDx Registers are Modbus Holding Registers available for use in your application. They can be accessed (read and written) by both the Modbus Master and the Microcontroller. The access can be individually or in block. Each register is 16 bits long and they are volatile RAM.

If your product is a sensor, these registers are typically written by the Microcontroller with sensed data, such as pressure, temperature, or humidity, and read by the Modbus Master.

 If the product is an actuator, these registers are usually written by the Modbus Master with control data, such as relay states (on/off), motor speed, or solenoid valve positions, and read by the Microcontroller.

These registers can also serve as a bidirectional data exchange point, allowing both the Modbus Master and the Microcontroller to read and write data.

* **Name:** HOLDx
* **Description:** Modbus Holding Registers
* **Address Range:** 0 to 499 (0x000 to 0x1F3)
* **Default value:** 0 (0x0000)
* **Memory Type:** Volatile RAM
* **Allowed values:** 0 to 65535 (0x00 to 0xFFFF)

| Bit 15 to Bit 8  | Bit 7 to Bit 0  |
| ---------------- | --------------- |
| HOLDx \[15 to 8] | HOLDx \[7 to 0] |