If my understanding is right. You can test the below conditions, which are BVA.

(If assumed the max length is 10)

1. Leave the field blank.(0)-If the requirement says the field is mandatory then this test should fail. If not should allow to leave it blank.

2. Enter any text with length max-1(9)

3. Enter any text with maximum length(10)

4. Enter any text with length max+1(11)

In Most cases ECP is not defined. But if its defined for example the requirement is A-Z,a-z and 0-9 are the only valid set.

Then you can test the below conditons:

1.It should give an error when a spl character is entered.

Depending on the priority of the the requirement. You can test different conditions like.a) having a spl char at start

b) having a spl char at the end. and etc.