MCP4641-104ESLASHST datasheet(60/92 Pages) MICROCHIP

60 / 92 page

MCP454X/456X/464X/466X

DS22107A-page 60

7.5

Read Data

Normal and High Voltage

The Read Command can be issued to both the Volatile

and Non-Volatile memory locations. The format of the

command, see Figure 7-4, includes the Start condition,

I2C Control Byte (with R/W bit set to “0”), A bit,

MCP4XXX Command Byte, A bit, followed by a

Repeated Start bit, I2C Control Byte (with R/W bit set to

“1”), and the MCP4XXX transmitting the requested

Data High Byte, and A bit, the Data Low Byte, the Mas-

ter generating the A, and Stop condition.

The I2C Control Byte requires the R/W bit equal to a

logic one (R/W = 1) to generate a read sequence. The

memory location read will be the last address

contained in a valid write MCP4XXX Command Byte or

address 00h if no write operations have occurred since

the device was reset (Power-on Reset or Brown-out

Reset).

During a write cycle (Write or High Voltage Write to a

Non-Volatile memory location) the Read command can

only read the Volatile memory locations. By reading the

Status Register (04h),

the Host Controller can

determine when the write cycle has completed (via the

state of the EEWA bit).

Read operations initially include the same address byte

sequence as the write sequence (shown in Figure 6-9).

This sequence is followed by another control byte

(including the Start condition and Ackowledge) with the

R/W bit equal to a logic one (R/W = 1) to indicate a

read. The MCP4XXX will then transmit the data con-

tained in the addressed register. This is followed by the

master generating an A bit in preparation for more data,

or an A bit followed by a Stop. The sequence is ended

with the master generating a Stop or Restart condition.

The internal address pointer is maintained. If this

address pointer is for a non-volatile memory address

and the read control byte addresses the device during

a Non-Volatile Write Cycle (tWC) the device will respond

with an A bit.

7.5.1

SINGLE READ

Figure 7-4 show the waveforms for a single read.

For single reads the master sends a STOP or

RESTART condition after the data byte is sent from the

slave.

7.5.1.1

Random Read

Figure 7-5 shows the sequence for a Random Reads.

Refer to Figure 7-5 for the random byte read

sequence.

7.5.2

CONTINUOUS READS

Continuous reads allows the devices memory to be

read quickly. Continuous reads are possible to all mem-

ory locations. If a non-volatile memory write cycle is

occurring, then Read commands may only access the

volatile memory locations.

Figure 7-6 shows the sequence for three continuous

reads.

For continuous reads, instead of transmitting a Stop

or Restart condition after the data transfer, the master

reads the next data byte. The sequence ends with the

master Not Acknowledging and then sending a Stop or

Restart.

7.5.3

THE HIGH VOLTAGE COMMAND

(HVC) SIGNAL

The

High

Voltage

Command

(HVC)

signal

multiplexed with Address 0 (A0) and is used to indicate

that the command, or sequence of commands, are in

the High Voltage mode. High Voltage commands allow

the device’s WiperLock Technology and write protect

features to be enabled and disabled.

The HVC pin has an internal resistor connection to the

MCP4XXXs internal VDD signal.

7.5.4

IGNORING AN I2C TRANSMISSION AND

“FALLING OFF” THE BUS

The MCP4XXX expects to receive entire, valid I2C

commands and will assume any command not defined

as a valid command is due to a bus corruption and will

enter a passive high condition on the SDA signal. All

signals will be ignored until the next valid Start

condition and Control Byte are received.

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