section 7 - Index of

are serially available to the external command controller through their common FIFO address.Figure 10-9 shows the block diagram of the PAB FIFO. The FIFO is not affected bythe operations performed during the debug mode except for the FIFO pointer incrementwhen reading the FIFO. When entering the debug mode, the FIFO counter will be pointingto the FIFO register containing the address of the oldest of the five executed instructions.The first FIFO read will obtain the oldest address and the following FIFO reads will get theother addresses from the oldest to the newest (the order of execution).To ensure FIFO coherence, a complete set of five reads of the FIFO must be performedbecause each read increments the FIFO pOinter, thus making it point to the next location.After five reads the pointer will point to the same location it pointed to before starting theread procedure.10.9 SERIAL PROTOCOL DESCRIPTIONThe following protocol permits an efficient means of communication between the OnCE'sexternal command controller and the DSP56K chip. Before starting any debugging activity,the external command controller must wait for an acknowledge on the DSO line, indicatingthat the chip has entered the debug mode. The external command controller communicateswith the chip by sending a-bit commands that may be accompanied by 24 bitsof data. Both commands and data are sent or received most significant bit first. After sendinga command, the external command controller must wait for the processor to acknowledgeexecution of the command before it may send a new command.When accessing OnCE 16-bit registers, the register contents appear in the 16 most significantbits in the 24-bit data field, and the a least significant bits are zeroed.10.9.1 OnCE CommandsThe OnCE commands may be classified as follows:• read commands (when the chip will deliver the required data).• write commands (when the chip will receive data and write the data in one of the OnCEregisters).• commands that do not have data transfers associated with them.-The commands are a bits long and have the format shown in Figure 10-4.10.10 DSP56K TARGET SITE DEBUG SYSTEM REQUIREMENTSA typical DSP56K debug environment consists of a target system where the DSP56K residesin the user defined hardware. The debug serial port interfaces to the external commandcontroller over a 6-wire link which includes the 4 OnCE wires, a ground, and a resetwire. The reset wire is optional and is only used to reset the DSP56K and its associatedcircuitry.