[ SN75176B ] Maximum number of nodes

Kenichiro

Other Parts Discussed in Thread: SN75176B

[ SN75176B ] Maximum number of nodes

Hi,

Can you help me to calculate / predict maximum number of nodes with SN75176B?
I have studied following post to understand how I can get the number. However it seems that SN75176B is not dedicated driver for RS-485 (also can support RS-422), so no unit load nor leakage current specification can be found from its datasheet.

RS-485 basics: how to calculate unit loads and the maximum number of nodes on your network
e2e.ti.com/.../rs-485-basics-how-to-calculate-unit-loads-and-the-maximum-number-of-nodes-on-your-network

I understand that the 32 nodes are still its maximum number from standard and figure 17.
However, it's helpful if you can share how I can calculate for this particular device, SN75176B.

Thanks,
Ken

over 7 years ago

0 Ron Michallick over 7 years ago

TI__Guru*** 139946 points

Ken,

In section 1 of front page and Electrical Characteristics table 7.5, Input resistance is stated as 12 k-ohm minimum.
This means SN75176B is 1 UL. If every device on bus is SN75176B then maximum is 32.
If not every device is SN75176B then add the UL numbers from all devices and make sure the total is less then 32.

0 Kenichiro over 7 years ago in reply to Ron Michallick

Mastermind 9165 points

Hi Ron,

Thank you for your feedback, this is good information for me!
(Now I can calculate nodes number for other devices, too)

BTW, is it required to place either pull-up or pull-down on TTL logic side to prevent open condition of pins?

Thank you for your support as always.
Regards,
Ken

0 Ron Michallick over 7 years ago in reply to Kenichiro

TI__Guru*** 139946 points

Ken,

The inputs will naturally float high, but valid level should be provided externally.
In what cases do you expect inputs to be open?

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[ SN75176B ] Maximum number of nodes

[ SN75176B ] Maximum number of nodes