Motorola 009 Instrukcja Użytkownika Pobierz pdf (Strona 15)

System Overview

System Operation

MOTOROLA

SHI Port Usage

2-3

2.1 SYSTEM OPERATION

A block diagram of the connections between DSP and MCU is shown in

Figure 2-1.

The

MCU is responsible for booting the DSP out of hardware reset, responding to user input,

and sending parameters to the DSP. In this application, the DSP only receives data from

the MCU. Hence, Master In Slave Out (MISO) is not a required connection for this

application. During boot, the data transmitted to the DSP are the opcodes for the DSP

program to be executed. After boot, the data transmitted to the DSP are values for the

DSP run-time application indicating which GPIO line the DSP should force high.

Figure 2-1

Block Diagram of the DSP-MCU System

The DSP operates as a slave device to the MCU. There are four connections between the

DSP and the MCU: SCK, MOSI, SS

, and HREQ. Of these, only the Host Request (HREQ)

is an output from the DSP. SCK is the Synchronous Bit Clock. Master Out Slave In

(MOSI) is the serial data input to the DSP. SS

is a Slave Select line that initiates the

transfer. HREQ

is used to indicate that the DSP is ready to receive a word.

Hence, if monitored by the MCU, the HREQ

line provides a method of hardware

handshaking between the two devices that yields a more robust interface. It is possible to

interface two devices without using the HREQ

line, but doing so requires careful design

of the master device's software to prevent transmitting data when the DSP slave is not

ready. By monitoring the HREQ

line, the MCU software can be certain the DSP is ready

to receive a word before transmitting it.

HREQ

SCK

MOSI

MISO

DSP56004

SHI

MCU

AA1415

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Motorola 009 Instrukcja Użytkownika Strona 15