Technical information

SCI to SPI Peripheral Communication in V850ES Microcontrollers

Figure 5. SPI Mode Control Register

01234567

CPOL CPHA

SPI Mode Control Register

CPHA = 0 First-edge of SCK Used as Data Capture Strobe

Falling-edge of SS_B Indicates Start of Transmission

CPHA = 1 First-edge of SCK Used as Data Drive Strobe

Slave-unit Uses First-edge of SCK as Start of Transmission

CPOL = 0 Idle-state of SCK = 0 Rising-edge of SCK = Active-edge

CPOL = 1 Idle-state of SCK = 1 Falling-edge of SCK = Active-edge

2.3 Comparison of NEC Electronics CSI and SPI Transfer Operations

The NEC Electronics CSI unit has a Clock Selection Register (CSICn), which specifies clocking method

using the CKPn and DAPn bits. The SPI unit has an SPI Control Register, which specifies clocking

method using the CPOL and CPHA bits. Table 2 shows a comparison of NEC Electronics CSI clocking

methods and those of the SPI.

Table 2. CSI and SPI Clocking Methods

NEC Electronics CSI Clocking Method SPI Clocking Method

CKPn DAPn Clocking Type Descriptions

CPOL CPHA Clocking Type Descriptions

Type 1 clocking method Idle state clock = 1

Idle state clock = 1 First edge SCK is data drive strobe

First edge SCK is data drive strobe

Type 2 clocking method Idle state clock = 1

Idle state clock = 1 First edge clock is data capture strobe

First edge clock is data capture strobe

Type 3 clocking method Idle state clock = 0

Idle state clock = 0 First edge clock is data drive strobe

First edge clock is data drive strobe

Type 4 clocking method Idle state clock = 0

Idle state clock = 0 First edge clock is data capture strobe

First edge clock is data capture strobe

In both NEC Electronics CSI and SPI communication, when the first edge SCK is used as the data capture

strobe, Chip Select (SS_B) is used as a "start of transmission" signal. In this case, the Chip Select pin

should be driven inactive and then active again between data transmissions, as shown in Figure 6.

When the first edge SCK is used as the data drive strobe, the first edge SCK is the start of transmission

signal. In this case, the Chip Select pin can remain in the active state between data transmissions.