| 摘要 |
A PABX which comprises a motherboard (1) and an ISDN card (2), both of which are provided with respective microprocessors (3,21), for controlling their respective operations. The microprocessor (21) of the ISDN card (2) operates independently of the microprocessor (3) of the motherboard (1). Communication between the motherboard (1) and the ISDN card (2) is through a mailbox circuit (43) which facilitates the transfer of messages between the motherboard (1) and the ISDN card (2) in packets of four bits, the four bit packets being transferred one at a time. Packets of a message received by the ISDN card (2) are stored in a receive buffer (44) until all the packets of the message have been received, and the message is then written into a RAM (23) of the ISDN card (2), for subsequent execution. Packets of a message received by the motherboard (1) are stored in a receiver buffer (9) until all the packets of a message are received, and the message is then written to a RAM (5) by the microprocessor (3) for subsequent execution. <Fig. 1> |
