TCN75 datasheet(8/20 Pages) MICROCHIP

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TCN75

DS21490C-page 8

4.0

SHUTDOWN MODE

When the appropriate bit is set in the configuration reg-

ister (CONFIG) the TCN75 enters its low-power Shut-

down mode (IDD = 1 μA, typical) and the temperature-

to-digital conversion process is halted. The TCN75’s

bus interface remains active and TEMP, TSET, and

THYST may be read from and written to. Transitions on

SDA or SCL due to external bus activity may increase

the standby power consumption. If the TCN75 is in

Interrupt mode, the state of INT/CMPTR will be reset

upon entering Shutdown mode.

4.1

Fault Queue

To lessen the probability of spurious activation of INT/

CMPTR the TCN75 may be programmed to filter out

transient events. This is done by programming the

desired value into the Fault Queue. Logic inside the

TCN75 will prevent the device from triggering INT/

CMPTR unless the programmed number of sequential

temperature-to-digital conversions yield the same

qualitative result. In other words, the value reported in

TEMP must remain above TSET or below THYST for the

consecutive number of cycles programmed in the Fault

Queue. Up to a six-cycle “filter” may be selected. See

Section 5.0

“Register

Set

and

Programmer’s

ModeL”, Register Set and Programmer’s Model.

4.2

Serial Port Operation

The Serial Clock input (SCL) and bidirectional data port

(SDA) form a 2-wire bidirectional serial port for pro-

gramming and interrogating the TCN75. The following

table indicates TCN75 conventions that are used in this

bus scheme.

TABLE 4-1:

SERIAL BUS CONVENTIONS

All transfers take place under control of a host, usually

a CPU or microcontroller, acting as the Master, which

provides the clock signal for all transfers. The TCN75

always operates as a Slave. This serial protocol is

illustrated in Figure 5-1. All data transfers have two

phases; and all bytes are transferred MSB first.

Accesses are initiated by a Start condition, followed by

a device address byte and one or more data bytes. The

device address byte includes a Read/Write selection

bit. Each access must be terminated by a Stop condi-

tion. A convention called Acknowledge (ACK) confirms

receipt of each byte. Note that SDA can change only

during periods when SCL is LOW (SDA changes while

SCL is HIGH are reserved for Start and Stop condi-

tions).

4.3

Start Condition (Start)

The TCN75 continuously monitors the SDA and SCL

lines for a Start condition (a HIGH-to-LOW transition of

SDA while SCL is HIGH), and will not respond until this

condition is met.

Term

Explanation

Transmitter

The device sending data to the bus.

Receiver

The device receiving data from the bus.

Master

The device which controls the bus: initiating

transfers (Start), generating the clock, and

terminating transfers (Stop).

Slave

The device addressed by the master.

Start

A unique condition signaling the beginning of

a transfer indicated by SDA falling (High –

Low) while SCL is high.

Stop

A unique condition signaling the end of a

transfer indicated by SDA rising (Low – High)

while SCL is high.

ACK

A Receiver acknowledges the receipt of each

byte with this unique condition. The Receiver

drives SDA low during SCL high of the ACK

clock-pulse. The Master provides the clock

pulse for the ACK cycle.

NOT Busy

When the bus is idle, both SDA & SCL will

remain high.

Data Valid

The state of SDA must remain stable during

the High period of SCL in order for a data bit

to be considered valid. SDA only changes

state while SCL is low during normal data

transfers. (See Start and Stop conditions).

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