Microchip Technology TSSOP20EV Data Sheet

DS22233A-page 58

© 2009 Microchip Technology Inc.

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 

.

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.

7.8.1

SINGLE DECREMENT 

Typically, the CS pin starts at the inactive state (V

IH

),

but may already be in the active state due to the
completion of another command. 

 through 

waveforms for a single Decrement. The decrement
operation requires that the CS pin be in the active state
(V

IL

or V

IHH

). Typically, the CS pin will be in the inactive

state (V

IH

) and is driven to the active state (V

IL

or V

IHH

).

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 command is disabled. If the Wiper register
has a Zero Scale value (000h), then the wiper value will
not decrement. See 

 for additional information

on the Decrement Command vs. the current volatile
wiper value.

The Decrement commands only require the Decrement
command byte, while the CS pin is active (V

IL

or V

IHH

)

for a single decrement. 

After the wiper is decremented to the desired position,
the CS pin should be forced to V

IH

 to ensure that

unexpected transitions on the SCK pin do not cause
the wiper setting to change. Driving the CS pin to V

IH

should occur as soon as possible (within device
specifications) after the last desired decrement occurs. 

 shows the valid addresses for

the Decrement Wiper command. Other
addresses are invalid. 

 

        

A
D

3

A
D

2

A
D

1

A
D

0

1

0

X

X

1

1

1

1

1

1

1*

1

Note 1, 2 

1

1

1

1

1

1

0

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 (V

IH

).

3FFh

081h

3FFh

101h

Reserved 
(Full Scale (W = A)) 

No

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

000h

Zero Scale (W = B)

No