The trading system of the Exchange is an order-driven system.

During the Pre-opening Session and the Closing Auction Session, the system accepts at-auction and at-auction limit orders only.

During the Continuous Trading Session, the system acceptslimit, enhanced limit and special limit orders only, with an option for an "All-or-Nothing Qualifier" that confines the order to be either executed immediately in full or rejected, without being written into the central order book.

For details of the trading system and associated infrastructure, please visit the Infrastructure section.

For all trading sessions, the maximum order size for automatch stocks is 3,000 board lots. The maximum number of orders in each price queue is 40,000 while the maximum number of outstanding orders per broker ID has been removed.

Pre-opening Session

Orders are accumulated over a certain period of time and matchedwithin a pre-defined random matching period. Orders are matched in order type, price and time priority (at-auction orders carry a higher matching priority), at the final Indicative Equilibrium Price ("IEP"). Please click here forFAQ in relation to Pre-opening Session.

For details of the POS Enhancements, please refer to the POS enhancements initiativeand POS information book.

Continuous Trading Session

Orders are continuously executed in strict price and time priority. An order entered into the system at an earlier time must be executed in full before an order at the same price entered at a later time is executed.

Closing Auction Session

The Closing Auction Session (CAS) is applicable to selected securities and consists of four periods: the Reference Price fixing period, order input period, no-cancellation period, and random closing period.

During the Reference Price fixing period, a Reference Price, which sets the allowable upper and lower price limits of the closing auction session ( 5 per cent from the Reference Price), is calculated for each security that will have a Closing Auction Session.

During the order input period, at-auction orders and at-auction limit orders within the 5 per cent price limit can be entered, amended or cancelled.

During the no-cancellation period, prices of new at-auction limit orders must be between the lowest ask and highest bid of the order book, and no orders can be amended or cancelled.

During the random closing period, the order rules from the no-cancellation period apply and the market closes randomly within two minutes. After the random closing period, orders for all CAS securities are matched at the final IEP. In cases where final IEP cannot be established during the CAS, the Reference Price will be treated as the final IEP for order matching and will become the closing price of the CAS security. Order matching is based on order type, price and then time priority (at-auction orders carry a higher matching priority).

For further detail of CAS, please refer to the CAS information book and infographic.

OTP-C currently supports the following order types for automatching:

Pre-opening Session and Closing Auction Session

The OTP-Conly accepts at-auction and at-auction limit orders during the Pre-opening Session and Closing Auction Session.

For Pre-opening Session, the order price input into the OTP-Ccannot deviate 9 times or more from the previous closing price or the nominal price (as the case may be), if available.

For Closing Auction Session, the order price input into the OTP-Cis subject to the two stages price limit. Stage 1 price limit: is applicable to the Order Input Period and is set at 5 per cent from the Reference Price. Stage 2 price limit is applicable to the No Cancellation Period and Random Closing Period and is set at the highest bid and the lowest ask of the order book at the end of the Order Input Period.