Motorola 009 User Manual download pdf (Page 16)

2-4

SHI Port Usage

MOTOROLA

System Overview

System Operation

A flow diagram that describes the interaction between the DSP and MCU is shown in

Figure 2-2

. The MCU system operation is shown on the left, while the DSP system

operation is shown on the right. Hardware reset is the initial event that starts the system.

Since the jumpers for the MODA, MODB, and MODC pins have been set to indicate SHI

boot in SPI mode, the DSP executes the SPI boot portion of the internal boot ROM

program. The DSP polls for data to be received on the SHI port.

The MCU, on the other hand, first checks the HREQ

pin to see if the DSP is ready to

receive data. When the MCU verifies that HREQ

is asserted, it transmits a data

word—one DSP program opcode. The DSP sees that a data word is available at the SHI

Host Receive (HRX) register and copies that word to DSP Program RAM. The MCU

continues to transmit data to the DSP until 512 words have been sent. The DSP in turn

fills its entire Program RAM with this data. Next, the boot program changes the

operating mode to enable Program RAM and executes the newly loaded program

starting at memory location

P:$0

. The DSP and MCU are now ready for steady state

operation of their programs and enter an idle state.

Both the DSP and the MCU await user input. When a button is pressed in the MCU user

interface (LCD menus), the MCU responds by transmitting a value to the DSP SHI port.

This transmission generates a DSP interrupt resulting in execution of the SHI interrupt

service routine. The SHI interrupt service routine receives the word from the HRX

GPIO pins will respond accordingly. The user's perception is that the a button was

pressed and a GPIO line was asserted. The DSP and MCU resume the idle states.

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Motorola 009 User Manual Page 16