Why need 2 types of services ?

[urchc_1533771]

In datasheet of BLE I read that exist 2 types of services:

   

Service type
 Primary – Represents the primary functionality of the device.
 Secondary – Represents an additional functionality of the device.

   

What exactly it mean ? Why need Secondary type ? Why not to use only Primary ?

[rola_264706]

Lets say you had a device that had two readings the Primary reading and a second reading.  Like a light detector with an intensity and color of the light.

[urchc_1533771]

How it`s sense to read/write characteristic ?

[Anonymous · Accepted solution]

A verbatim from the BLE Spec: "A primary service is a service that provides the primary functionality of a device. A secondary service
is a service that provides auxiliary functionality of a device and is referenced from at least one primary service on the device. A secondary service is a service that is only intended to be referenced from a primary service or another secondary service or other higher layer specification. A secondary service is only relevant in the context of the entity that references it."

   

Coming to writing/reading the characteristics in these services, there are no differences between the two. You can read/write to characteristics in secondary service just as characteristics in the primary service.