UPDATE 1-Datatec sees H1 headline EPS lower

* Generated $1.8 bln in revenues, margins stable

* Unrealised expense of $6.4 mln vs $16.8 mln gain

(Adds details)

JOHANNESBURG, Sept 30 (Reuters) - South African IT firm Datatec Ltd (DTCJ.J) (DTC.L) expects to report a drop in interim headline earnings per share, but sees its gross margins remaining stable.

The company, which is listed in London and Johannesburg and is a distributor for companies such as Cisco, said on Wednesday it expected headline earnings per share for the six months to end August to be between 4-5 U.S. cents compared to 17.6 cents in the previous period.

The company said it had generated $1.8 billion in revenues in the six month period.

But Datatec added that an increase in the fair value of put option liabilities had resulted in an unrealised additional expense of $6.4 million versus a gain of $16.8 million in the previous period.

The company said excluding this expense, its EPS and headline EPS would have been between 8-9 U.S. cents per share.

The company will publish its interim results on October 14.

EPS and headline EPS are South Africa's main profit gauge. (Reporting by Gugulakhe Lourie)