Renesas Asynchronous SH7145F Installation and operating instructions

APPLICATION NOTE

REJ06B0357-0100O/Rev.1.00 March 2004 Page 1 of 17

SH7145F

Asynchronous Serial Data Transmission/Reception

Summary

The SH7144 series is a single-chip microprocessor based on the SH-2 RISC (Reduced Instruction

Set Computer) CPU core and integrating a number of peripheral functions.

This application note describes asynchronous serial data transmission/reception using the SCI

(Serial Communication Interface) module of the SH7145F. It is intended to be used as reference

by users designing software applications.

The program examples contained in this application note have been tested. However, operation

should be confirmed before using them in an actual application.

Device for Which Operation Has Been Confirmed

SH7145F

Contents

1. Specifications................................................................................................ 2

2 Functions Used............................................................................................. 3

3. Operation....................................................................................................... 6

4. Software........................................................................................................ 8

5. Flowcharts..................................................................................................... 11

6. Program Listing............................................................................................. 14

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Asynchronous Serial Data Transmission/Reception

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1. Specifications

As shown in figure 1, asynchronous serial data transmission is performed using channel 1 (ch1) of

the SCI module of the SH7145F. In this task example 3 bytes of serial data are received by the

SH7145, and the receive data is then transmitted. The communication format is 192,000 bps, 8-

bit, one stop bit, and no parity.

SH7145

Serial data

transfer

target MCU

TXD RXD

SCI

(ch1)

3.3 V 3.3 V

TXD

RXD

Figure 1 Asynchronous Serial Data Transmission/Reception by SH7145

Table 1 Asynchronous Serial Data Transmission Format

Format Item Setting

Bit rate 19200 bps

Data length 8 bits

Parity bit No

Stop bit 1 bit

Serial/parallel conversion format LSB first

SH7145F

Asynchronous Serial Data Transmission/Reception

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2 Functions Used

In this task example the SCI (Serial Communication Interface) is used to perform asynchronous

serial data transmission/reception. Figure 2 shows a block diagram of channel 1 (ch1) of the SCI

module. The functions of the elements shown in figure 2 are described below.

TEI_1

TXI_1

RXI_1

ERI_1

SCI1 clock I/O pin

(SCK1)

SCI1 transmit data

output pin

(TXD1)

SCI1 receive data

input pin

(RXD1)

SCI0 synchronous serial transfer function block

Baud rate generator Bit rate register 1

(BRR_1)

Clock Transmit/receive operation control settings

Transfer rate generator

Serial mode register 1

(SMR_1)

Serial control register 1

(SCR_1)

Serial status register 1

(SSR_1)

Serial direction control register 1

(SDCR_1)

Transmit/receive

control circuit

Interrupt

requests

Transmit data control

Transmit shift register 1

(TSR_1) Transmit data register 1

(TDR_1)

Receive data control

Receive shift register 1

(RSR_1) Receive data register 1

(RDR_1)

External

clock

Pφ/128

Pφ/32

Pφ/8

Pφ1

On-chip

peripheral cloc

Figure 2 SCI (ch1) Block Diagram

•Asynchronous Mode

Serial data communication is performed using synchronization by character unit. This allows

serial communication with a standard dedicated asynchronous communication chip such as a

Universal Asynchronous Receiver/Transmitter (UART) or Asynchronous Communication

Interface Adapter (ACIA). In addition, the asynchronous mode supports serial communication

among multiple processors (multiprocessor communication function).

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Asynchronous Serial Data Transmission/Reception

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•On-Chip Peripheral Clock Pφ

This is the reference clock for operation of on-chip peripheral functions. The clock signal is

generated by a clock oscillator.

•Receive Shift Register (RSR_1)

This register is used to receive serial data. Serial data is input to RSR_1 from the RxD_1 pin.

When one frame of data has been received, it is automatically transferred to the receive data

•Receive Data Register (RDR_1)

Received data is stored in this 8-bit register. When one frame of data has been received, it is

automatically transferred from RSR_1. RSR_1 and RDR_1 are in a double-buffer

configuration, allowing continuous reception of data. RDR_1 is a receive-only register, so it

can only be read by the CPU.

•Transmit Shift Register (TSR_1)

This register is used to transmit serial data. In order to transmit data, the data is first

transferred from the transmit data register (TDR_1) to TSR_1. Then the transmit data is

output from the TxD_1 pin. TSR_1 cannot be accessed directly by the CPU.

•Transmit Data Register (TDR_1)

Data to be transmitted is stored in this 8-bit register. When it is detected that TDR_1 is empty,

data that has been written to TDR_1 is automatically transferred to TSR_1. TDR_1 and

TSR_1 are in a double-buffer configuration. This allows data to be transferred to TSR_1 after

one frame of data has been transmitted and the next frame of data is still being written to

TDR_1, making possible continuous transmission of data. It is always possible to read or

write to the TDR from the CPU, but before writing to the TDR it should be confirmed that the

value of the TDRE bit in the serial status register (SSR_1) is 1.

•Serial Mode Register (SMR_1)

This 8-bit register is used to select the serial data communication format and the clock source

for the on-chip baud rate generator.

•Serial Control Register (SCR_1)

This register is used for transmit and receive control, interrupt control, and to select the

transmit and receive clock source.

•Serial Status Register (SSR_1)

This register comprises the SCI1 status flag and the transmit and receive multiprocessor bits.

TDRE, RDRF, ORER, PER, and FER can be cleared only.

•Serial Direction Control Register (SDCR_1)

This register is used to select whether the LSB or MSB is first. For 8-bit communication

either LSB-first or MSB-first may be selected, but LSB-first should be used for 7-bit

communication.

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Asynchronous Serial Data Transmission/Reception

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•Bit Rate Register (BRR_1)

This 8-bit register is used to adjust the bit rate. The SCI has independent baud rate generators

for the individual channels, allowing different bit rates to be set for each. See the hardware

manual for details on setting values, execution rate relationships, etc.

Table 2 shows the function allocations for the task example.

Table 2 Function Allocations

Function Classification Function Allocation

TXD1 Pin Channel 1 transmit data output pin

RXD1 Pin Channel 1 transmit data input pin

SMR_1 SCI1 Sets communication format to asynchronous mode

SCR_1 SCI1 Enables transmit operation

SSR_1 SCI1 Status flag showing SCI1 operation status

SDCR_1 SCI1 Specifies LSB-first

BRR_1 SCI1 Sets communication bit rate

TSR_1 SCI1 Register for transmitting serial data

TDR_1 SCI1 Register for storing transmit data

RSR_1 SCI1 Register for receiving serial data

RDR_1 SCI1 Register for storing receive data

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3. Operation

Figure 3 shows the operation of asynchronous mode data transmission in the task example. To

help explain figure 3, table 3 lists the software and hardware processing that is performed.

(1)

(2) (3)

(4)(5) (6)

(7) (8) (9)

(10) (11)

(12)(13)(14)

(15)

Data bits D0 to D7

TxD1

(pin)

TDR_1

(register)

TSR_1

(register)

TXD1

(pin)

TDRE

(SSR_1 bit)

RDRF

(SSR_1 bit)

Receive operation

Notes: 1. The start bit, transmit data, parity bit, and stop bit are output, in that order, from the TxD1 pin.

2. To perform continuous reception, read data transferred to RDR until reception of next data is

complete.

Transmit operation

Start

bit

Start

bit

Start

bit

Stop

bit

Data

bits

Figure 3 Data Transmission Operation

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Table 3 Processing

Software Processing Hardware Processing

(1) — RSR_1 receives serial data and transfers it

to RDR_1

(2) — Set RDRF flag in SSR_1 to 1

(3) Read data from RDR_1

(4) Clear RDRF flag in SSR_1 to 0

(5) WritereceivedatatoTDR_1 —

(6) Clear TDRE flag in SSR_1 to 1 —

(7) — TransferdatafromTDR_1toTSR_1

(8) — Set TDRE flag in SSR_1 to 1 and output

transmit data from pin TXD1

(9) — RSR_1 receives serial data and transfers it

to RDR_1

(10) — Set RDRF flag in SSR_1 to 1

(11) Read data from RDR_1

(12) Clear RDRF flag in SSR_1 to 0

(13) Write receive data to TDR_1 —

(14) Clear TDRE flag in SSR_1 to 1 —

(15) — Transfer data from TDR_1 to TSR_1

(16) Repeat Repeat

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4. Software

(1) Module Descriptions

Table 4 lists the modules used in the task example.

Table 4 Module Descriptions

Module Label Function

Main routine main Calls modules

SCI routine init_sci Initial settings of SCI1

Receive routine rcv_sci Receives serial data

Transmit routine trans_sci Transmits serial data

Error handling err_int Handles receive errors

(2) Argument Descriptions

Table 5 lists the arguments used in the task example.

Table 5 Argument Descriptions

Argument Function Module

Rev_data[0–2] Stores SCI_1 receive data Receive routine

trans_data Transmits data from SCI_1 Transmit routine

(3) On-Chip Register Descriptions

Table 6 lists the on-chip registers used in the task example. The set values shown are the values

used in the task example and differ from the initial settings.

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Asynchronous Serial Data Transmission/Reception

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Table 6 On-Chip Register Descriptions

Bit Set Value Function

MSTCR1 MSTP17 0 Module standby control register 1

SCI1 standby control bit

Standby cancelled when MSTP17 = 0

SCR_1 H'70 Serial control register 1 (SCI_1)

Transmit and receive control, interrupt control, transmit and receive

clock source control

TIE 0 Transmit interrupt enable

TXI interrupt requests enabled when set to 1

RIE 1 Receive interrupt enable

RXI and ERI interrupt requests enabled when set to 1

TE 1 Transmit enable

Transmit operations enabled when set to 1

RE 1 Receive enable

Receive operations enabled when set to 1

MPIE 0 Multiprocessor interrupt enable

(In asynchronous mode, enabled when MP = 1 in SMR)

In the task example, disabled because MP = 0

TEIE 0 Transmit end interrupt enable

TEI interrupt requests enabled when set to 1

CKE1

CKE2

Clock enable 1, 0

Selects clock source and SCK pin function

In the task example, clock source is on-chip clock and SCK pin is not

used

SMR_1 H'00 Serial mode register 1

Selects communication format and the clock source for on-chip baud

rate generator

C/A 0 Communication mode

Asynchronous mode when cleared to 0

CHR 0 Character length (enabled in asynchronous mode only)

8-bit transmission and reception when 0

PE 0 Parity enable (enabled in asynchronous mode only)

No-parity transmission and reception when 0

O/E 0 Parity mode (enabled in asynchronous mode when PE = 1)

(In this example PE = 0 and this bit is disabled)

STOP 0 Stop bit length (enabled in asynchronous mode only)

1-stop-bit transmission and reception when 0

SH7145F

Asynchronous Serial Data Transmission/Reception

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Bit Set Value Function

SMR_1 MP 0 Multiprocessor mode (enabled in asynchronous mode only)

Multiprocessor communication disabled when 0

CKS1

CKS2

Clock select 1, 0

When value is 00, Pφclock selected using on-chip baud rate generator

as clock source

BRR_1 H'40 Bit rate register 1

8-bit register for adjusting bit rate

SDCR_1 H'F2 Serial direction control register 1

DIR bit (bit 3) selects LSB-first or MSB-first

In task example, DIR = 0 (LSB-first)

SSR_1 H'xx Serial status register 1

Comprises SCI1 status flag and transmit and receive multiprocessor bits

Only 0 may be written to the status flag, to clear it

TDRE *Transmit data register empty (status flag)

RDRF *Receive data register full (status flag)

ORER *Overrun error (status flag)

FER *Framing error (status flag)

PER *Parity error (status flag)

TEND *Transmit end (status flag)

MPB 0 Multiprocessor bit

MPBT 0 Multiprocessor bit transfer

PA4MD1

PA4MD0

Port A control register L2

Function setting for port A multiplex pin (TXD1)

PACRL2

PA3MD1

PA3MD0

Port A control register L2

Function setting for port A multiplex pin (RXD1)

*: Can only be cleared to 0. Setting to 1 is performed by hardware.

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