Production Data

WM8213

w

PD Rev 4.1 July 2008

23

LINE-BY-LINE OPERATION

Certain linear sensors give colour output on a line-by-line basis. i.e. a full line of red pixels followed

by a line of green pixels followed by a line of blue pixels. Often the sensor will have only a single

output onto which these outputs are time multiplexed.

The WM8213 can accommodate this type of input by setting the LINEBYLINE register bit high.

When in this mode the green and blue input PGAs are disabled to save power. The analogue input

signal should be connected to the RINP pin. The offset and gain values that are applied to the Red

input channel can be selected, by internal multiplexers, to come from the Red, Green or Blue offset

and gain registers. This allows the gain and offset values for each of the input colours to be setup

individually at the start of a scan.

When register bit ACYC=0 the gain and offset multiplexers are controlled via the INTM[1:0] register

bits. When INTM=00 the red offset and gain control registers are used to control the Red input

channel, INTM=01 selects the green offset and gain registers and INTM=10 selects the blue offset

and gain registers to control the Red input channel.

When register bit ACYC=1, ‘auto-cycling’ is enabled, and the input channel switches to the next

offset and gain registers in the sequence when a pulse is applied to the RSMP input pin. The

sequence is Red

→ Green → Blue → Red… offset and gain registers applied to the single input

channel. A write to the Auto-cycle reset register (address 05h) will reset the sequence to a known

state (Red registers selected).

When auto-cycling is enabled, the RSMP pin cannot be used to control reset level clamping. The

CLMPCTRL bit may be used instead (enabled when high, disabled when low).

NB, when auto-cycling is enabled, the RSMP pin cannot be used for reset sampling (i.e. CDS must

be set to 0).

CONTROL INTERFACE

The internal control registers are programmable via the serial digital control interface. The register

contents can be read back via the serial interface on pin OP[7]/SDO.

Note: It is recommended that a software reset is carried out after the power-up sequence, before

writing to any other register. This ensures that all registers are set to their default values (as shown

in Table 7).

SERIAL INTERFACE: REGISTER WRITE

Figure 18 shows register writing in serial mode. Three pins, SCK, SDI and SEN are used. A six-bit

address (a5, 0, a3, a2, a1, a0) is clocked in through SDI, MSB first, followed by an eight-bit data

word (b7, b6, b5, b4, b3, b2, b1, b0), also MSB first. Each bit is latched on the rising edge of SCK.

When the data has been shifted into the device, a pulse is applied to SEN to transfer the data to the

appropriate internal register. Note all valid registers have address bit a4 equal to 0 in write mode.

SCK

SEN

SDI

a5

0

a3a2a1

a0b7b6b5

b4b3b2b1b0

Address

Data Word

Figure 18 Serial Interface Register Write

A software reset is carried out by writing to Address “000100” with any value of data, (i.e. Data Word

= XXXXXXXX).