todha, page-3

Stop looking,I have found the answer. These securities have mortgages over properties used by TIM for MIS.The security ratio has to be below about 65% before covenants are breached.Income is from rental to TIM.Looks like the rental income will be in jeopardy but the security still looks adequate.(particularly at today's price)
They have been buying back these debentures with excess liquidity so this also will help the asset cover.
I have some but would not buy more as this may be a long drawn-out repayment situation if TIM bring in the receivers.