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AS1108

Data Sheet

Digit- and Control-Registers

Feature Register (0xXE)

The Feature Register is used for switching the device into external clock mode, applying an external reset, selecting

code-B or HEX decoding, enabling or disabling blinking, enabling or disabling the SPI-compatible interface, setting the

blinking rate, and resetting the blink timing.

Note: At power-up the Feature Register is initialized to 0.

No-Op Register (0xX0)

The No-Op Register is used when multiple AS1108 devices are cascaded in order to support displays with more than 4

digits. The cascading must be done in such a way that all DOUT pins are connected to DIN of the next AS1108 (see

Figure 11 on page 14). The LOAD/CSN and CLK signals are connected to all devices.

For example, if five devices are cascaded, in order to perform a write operation to the fifth device, the write-command

must be followed by four no-operation commands. When the LOAD/CSN signal goes high, all shift registers are

latched. The first four devices will receive no-operation commands and only the fifth device will receive the intended

operation command, and subsequently update its register.

Table 16. Feature Register Summary

D7

D6

D5

D4

D3

D2

D1

D0

blink_

start

sync

blink_

freq_sel

blink_en

spi_en

decode_sel

reg_res

clk_en

Table 17. Feature Register Bit Descriptions (Address (HEX) = 0xXE))

Addr: 0xXE

Feature Register

Enables and disables various device features.

Bit

Bit Name

Default

Access

Bit Description

D0

clk_en

0R/W

External clock select.

0 = Internal oscillator is used for system clock.

1 = Pin CLK of the serial interface operates as system clock input.

D1

reg_res

0R/W

Resets all control registers except the Feature Register.

0 = Reset Disabled. Normal operation.

1 = All control registers are reset to default state (except the Feature

Register) identically after power-up.

Note: The Digit Registers maintain their data.

D2

decode_sel

0R/W

Selects display decoding.

0 = Enable Code-B decoding (see Table 9 on page 8).

1 = Enable HEX decoding (see Table 10 on page 9).

D3

spi_en

0R/W

Enables the SPI-compatible interface.

0 = Disable SPI-compatible interface.

1 = Enable the SPI-compatible interface.

D4

blink_en

0R/W

Enables blinking.

0 = Disable blinking.

1 = Enable blinking.

D5 blink_freq_sel

0R/W

Sets blink with low frequency (with the internal oscillator enabled):

0 = Blink period typically is 1 second (0.5s on, 0.5s off).

1 = Blink period is 2 seconds (1s on, 1s off).

D6

sync

0R/W

Synchronizes blinking on the rising edge of pin LOAD/CSN. The

multiplex and blink timing counter is cleared on the rising edge of pin

LOAD/CSN. By setting this bit in multiple AS1108 devices, the blink

timing can be synchronized across all the devices.

D7

blink_start

0R/W

Start Blinking with display enabled phase. When bit D4 (blink_en) is set,

bit D7 determines how blinking starts.

0 = Blinking starts with the display turned off.

1 = Blinking starts with the display turned on.