MCP433X datasheet(61/88 Pages) MICROCHIP

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DS22242A-page 61

MCP433X/435X

7.8

Decrement Wiper

Normal and High Voltage

The Decrement command is an 8-bit command. The

Decrement command can only be issued to volatile

memory locations. The format of the command is

shown in Figure 7-6.

A Decrement command to the volatile memory location

changes that location after a properly formatted

command (8 clocks) have been received.

Decrement commands provide a quick and easy

method to modify the value of the volatile wiper location

by -1 with minimal overhead.

FIGURE 7-8:

Decrement Command –

SDI and SDO States.

7.8.1

SINGLE DECREMENT

Typically, the CS pin starts at the inactive state (VIH),

but may already be in the active state due to the

completion of another command.

Figure 6-4

through

Figure 6-5

show

possible

waveforms for a single decrement. The decrement

operation requires that the CS pin be in the active state

(VILor VIHH). Typically, the CS pin will be in the inactive

state (VIH) and is driven to the active state (VILor VIHH).

Then the 8-bit Decrement command (command byte) is

clocked in on the SDI pin by the SCK pins. The SDO pin

drives the CMDERR bit on the 7th clock.

The wiper value will decrement from the wiper’s full

scale value (100h on 8-bit devices and 80h on 7-bit

devices). Above the wiper’s full scale value (8-bit =

101h to 1FFh, 7-bit = 81h to FFh), the Decrement com-

mand is disabled. If the wiper register has a zero scale

value (000h), then the wiper value will not decrement.

See Table 7-5 for additional information on the Decre-

ment command vs. the current volatile wiper value.

The Decrement commands only require the Decrement

command byte, while the CS pin is active (VILor VIHH)

for a single decrement.

After the wiper is decremented to the desired position,

the CS pin should be forced to VIH to ensure that

unexpected transitions on the SCK pin do not cause

the wiper setting to change. Driving the CS pin to VIH

should occur as soon as possible (within device

specifications) after the last desired decrement occurs.

Note:

Table 7-2 shows the valid addresses for

the Decrement Wiper command. Other

addresses are invalid.

111111 1* 1 Note 1, 2

111111

0 Note 1, 3

(DECR COMMAND (n+1))

SDI

SDO

COMMAND BYTE

Note 1: Only functions when writing the volatile

wiper registers (AD3:AD0) 0h and 1h.

2: Valid Address/Command combination.

3: Invalid Address/Command combination

all following SDO bits will be low until the

CMDERR condition is cleared.

(the CS pin is forced to the inactive

state).

4: If a Command Error (CMDERR) occurs

at this bit location (*), then all following

SDO bits will be driven low until the CS

pin is driven inactive (VIH).

TABLE 7-5:

DECREMENT OPERATION VS.

VOLATILE WIPER VALUE

Current Wiper

Setting

Wiper (W)

Properties

Decrement

Command

Operates?

7-bit

Pot

8-bit

Pot

3FFh

081h

3FFh

101h

Reserved

(Full Scale (W = A))

080h

100h

Full Scale (W = A)

Yes

07Fh

041h

0FFh

081

W = N

040h

080h

W = N (Mid-scale)

Yes

03Fh

001h

07Fh

001

W = N

000h

Zero Scale (W = B)

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