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Serial Control Port Configuration

CS485xx Hardware User’s Manual

Figure 3-7. Repeated Start Condition with ACK and NACK

3.2.2.2 I

C Messaging

Messaging to the CS485xx using the I

C bus requires usage of all the information provided in the above I

Section 3.2.2 “I

C System Bus Description” on page 3-3 and Section 3.2.2.1 “I

C Bus Dynamics” on page

3-4. Every I

C transaction to the CS485xx will involve 4-byte words - for control and application image

download. A detailed description of the serial SPI communication mode is provided in this section. This

includes:

• A flow diagram and description for a serial I

C write

• A flow diagram and description for a serial I

C read

3.2.2.2.1 SCP_BSY Behavior

The SCP_BSY signal is not part of the I

C protocol, but it is provided so that the slave can signal to the

master that it cannot receive any more data. It performs the same function as that of holding SCP_CLK low

to halt transmission. A falling edge of the SCP_BSY

signal indicates the master must halt transmission.

Once the SCP_BSY

signal goes high, the suspended transaction may continue. It is important for the host to

obey the SCP_BSY

pin status for proper communication with the DSP.

3.2.2.3 Performing a Serial I

C Write

Information provided in this section is intended as a functional description indicating how to use the

configured serial control port to perform a I

C write from an external device (master) to the CS485xx DSP

(slave). The system designer must ensure that all timing constraints of the I

C write cycle are met (see the

CS485xx datasheet for timing specifications). When writing to the CS485xx, the same protocol described in

this section will be used when writing single-word messages to the boot firmware, writing multiple-word

overlay images to the boot firmware, and writing multiple-word messages to application firmware. The

examples given can therefor be expanded to fit any I

C writing situation.

The flow diagram shown in Figure 3-8 below, illustrates the sequence of events that define the I

C write

protocol for SCP. This protocol is discussed in the high-level procedure in Section 3.2.2.3.1.

SCP_CLK

SCP_SDA

Data Byte

ACK

Start

A[6] A[5] A[4] A[3] A[2] A[1] A[0] R/W

ACK

M S M S

rite

S M M S

ead