The main addition to the design is the use of socalled control characters in the data stream sent from AORTA Transmitter to AORTA Receiver. The Cypress HOTLink Transmitter and Receiver chips used to convert parallel data into a serial bitstream (on AORTA-T) and vice versa (on AORTA-R) in principle is used to send 8-bits data items, but some 9-bits data items (with 9th databit set to 1) also can be encoded and decoded; we call these data items here: control characters; some of these control characters are reserved for use by the HOTLink chips and a small number of them is available to the user.
The AORTA-T and AORTA-R have been made capable of sending and receiving control characters; on the receiving AORTA-R side the reception of a control character can be set to generate an interrupt.
NOTE: when reading data from the AORTA-R only 8 bits are read from the 9-bits wide data FIFO-chips (the 4 data FIFO-chips can be read out as either an 8Kx8 bit FIFO, a 4Kx16 bit FIFO or an 2Kx32 bits FIFO; with every read-cycle the user can select any of these 3 FIFO 'modes'); the 9th bit of the last data item read from each FIFO-chip (which when set signifies the data item is a control character) can be read from the statusregister (see table 4).