Is the TP-Link a bridged ADSL modem or something like that? Are you trying to access the TP-Link bridged ADSL modem from the networks behind the Mikrotik?
My modem is 10.1.1.1 and I created my network on the interface it plugs into on the Mikrotik to 10.1.1.2, and I can access my bridged TP-Link ADSL modem from my internal networks. So I can see it's Sync rate etc..
Hope output below helps you..
[admin@MikroTik] > interface print
Flags: D - dynamic, X - disabled, R - running, S - slave
# NAME TYPE ACTUAL-MTU L2MTU MAX-L2MTU
0 R ;;; WAN - 10.1.1.0
ether1 ether 1500 1520 1520
[admin@MikroTik] > /ip address print
Flags: X - disabled, I - invalid, D - dynamic
# ADDRESS NETWORK INTERFACE
3 10.1.1.2/24 10.1.1.0 ether1