> For the complete documentation index, see [llms.txt](https://diamondsystems.gitbook.io/user-manuals/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://diamondsystems.gitbook.io/user-manuals/sbcs/helios/hardware-user-manual/digital-io-ports.md).

# 21. DIGITAL I/O PORTS

Helios has two groups of digital I/O ports and one digital interrupt circuit: 

* 3 8-bit ports named A, B, and C are included in the data acquisition circuit on the AV model and are available on connector J17 on that model. 
* 2 8-bit ports named D and E are provided by the digital I/O circuit integrated into the Vortex processor and are available on connector J7 on all models. 
* An interrupt on the ISA bus may be triggered using the EXTTRIG pin on connector J17 on the AV model