Motorola DSP56000 manual Chip Status Information, OS1 OS0, Debug Serial Output DSO

ON-CHIP EMULATION (OnCE) PINS

10.2.2 Debug Serial Clock/Chip Status 1 (DSCK/OS1)

The DSCK/OS1 pin supplies the serial clock to the OnCE when it is an input. The serial clock provides pulses required to shift data into and out of the OnCE serial port. (Data is clocked into the OnCE on the falling edge and is clocked out of the OnCE serial port on the rising edge.) The debug serial clock frequency must be no greater than 1/8 of the pro- cessor clock frequency. When an output, this pin, in conjunction with the OS0 pin, provides information about the chip status (see Table 10-1). The DSCK/OS1 pin is an out- put when the chip is not in debug mode. When switching from output to input, the pin is three-stated. During hardware reset, this pin is defined as an output and it is driven low.

Note: To avoid possible glitches, an external pull-down resistor should be attached to this pin.

Table 10-1 Chip Status Information

OS1	OS0			Status
0	0	Normal State
0	1	Stop or Wait State
1	0	Chip waits for bus mastership
1	1	Chip waits for end of memory wait states
		(due to		assertion or BCR)
			WT

10.2.3 Debug Serial Output (DSO)

Serial data is read from the OnCE through the DSO pin, as specified by the last command received from the external command controller. Data is always shifted out the OnCE serial port most significant bit (MSB) first. Data is clocked out of the OnCE serial port on the ris- ing edge of DSCK.

The DSO pin also provides acknowledge pulses to the external command controller. When the chip enters the debug mode, the DSO pin will be pulsed low to indicate (ac- knowledge) that the OnCE is waiting for commands. After receiving a read command, the DSO pin will be pulsed low to indicate that the requested data is available and the OnCE serial port is ready to receive clocks in order to deliver the data. After receiving a write command, the DSO pin will be pulsed low to indicate that the OnCE serial port is ready to receive the data to be written; after the data is written, another acknowledge pulse will be provided.

During hardware reset and when the processor is idle, the DSO pin is held high.

10- 6 ON-CHIP EMULATION (OnCE) MOTOROLA