AT89LP6440 datasheet(115/194 Pages) ATMEL

115 / 194 page

115

3706A–MICRO–9/09

AT89LP6440 - Preliminary

SLA: Slave Address

In Figure 18-11 to Figure 18-14, circles are used to indicate that the TWIF flag is set. The num-

bers in the circles show the status code held in TWSR. At these points, actions must be taken by

the application to continue or complete the TWI transfer. The TWI transfer is suspended until the

TWIF flag is cleared by software.

When the TWIF flag is set, the status code in TWSR is used to determine the appropriate soft-

ware action. For each status code, the required software action and details of the following serial

transfer are given in Table 18-6 to Table 18-9.

18.6.1

Master Transmitter Mode

In the Master Transmitter mode, a number of data bytes are transmitted to a Slave Receiver. In

order to enter a Master mode, a START condition must be transmitted. The format of the follow-

ing address packet determines whether Master Transmitter or Master Receiver mode is to be

entered. If SLA+W is transmitted, MT mode is entered, if SLA+R is transmitted, MR mode is

entered.

A START condition is sent by writing the following value to TWCR:

TWEN must be set to enable the Two-wire Serial Interface, STA must be written to one to trans-

mit a START condition and TWIF must be cleared. The TWI will then test the Two-wire Serial

Bus and generate a START condition as soon as the bus becomes free. After a START condi-

tion has been transmitted, the TWIF flag is set by hardware, and the status code in TWSR will be

08h (see Table 18-6). In order to enter MT mode, SLA+W must be transmitted. This is done by

writing SLA+W to TWDR. Thereafter the TWIF bit should be cleared to continue the transfer.

When SLA+W has been transmitted and an acknowledgment bit has been received, TWIF is set

again and a number of status codes in TWSR are possible. Possible status codes in Master

mode are 18h, 20h, or 38h. The appropriate action to be taken for each of these status codes is

detailed in Table 18-6.

After SLA+W has been successfully transmitted, a data packet should be transmitted. This is

done by writing the data byte to TWDR. TWDR must only be written when TWIF is high. If not,

the access will be discarded and the previous value will be transmitted. After updating TWDR,

the TWIF bit should be cleared to continue the transfer. This scheme is repeated until the last

byte has been sent and the transfer is ended by generating a STOP condition or a repeated

START condition. A STOP condition is generated by writing the following value to TWCR:

A REPEATED START condition is generated by writing the following value to TWCR:

After a repeated START condition (status 10h) the Two-wire Serial Interface can access the

same slave again, or a new slave without transmitting a STOP condition. Repeated START

enables the master to switch between slaves, Master Transmitter mode and Master Receiver

mode without losing control of the bus.

TWCR

–TWEN

STA

STO

TWIF

–

Value

110

TWCR

–TWEN

STA

STO

TWIF

–

Value

101

TWCR

–TWEN

STA

STO

TWIF

–

Value

110

AT89LP6440 Datasheet(PDF) 115 Page - ATMEL Corporation

AT89LP6440 Datasheet(HTML) 115 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL