DS2149

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9. SOFTWARE MODE

The DS2149 operates in software mode when the MODE1 pin is pulled high. In software mode, a

microprocessor controls the device and reads its status through the serial port, which provides access to

the internal registers. The host processor can completely configure the device as well as get diagnostics

and status reports through the serial port. In NRZ mode, bipolar violation insertions and logic error

insertions are controlled by the BPV and INSLER pins. Similarly, the recovered clock, data, and BPV

detection are available only at output pins. All other mode settings and diagnostic information are

available through the serial port. Figure 9-1 and Figure 9-2 show the serial port data structure. The

registers are accessible through a 16-bit word composed of an 8-bit command and address byte and a

subsequent 8-bit data byte. Software mode allows control of the output timing. The CLKE pin determines

when SDO is valid relative to SCLK and when receive data is valid relative to RCLK.

9.1 Interrupt Handling

In software mode, the DS2149 provides a latched interrupt output pin. When enabled, a change in any of

the status register bits generates an interrupt. When an interrupt occurs, the INT output pin is driven low.

The INT output pin structure is an open-drain only. Each device that shares the INT line requires an

external pullup resistor. The interrupt is cleared when the interrupt condition no longer exists, and a 1 is

written to the appropriate bit in the interrupt mask register. Leaving a 1 in any of the bits in the interrupt

mask register masks that interrupt. Clearing that bit re-enables the interrupt.

Table 9-A. CLKE Pin Selection

CLKE PIN

OUTPUT

OUTPUT UPDATED ON

RPOS

RNEG

RDATA

Falling RCLK

LOW

SDO

Rising SCLK

RPOS

RNEG

RDATA

Rising RCLK

HIGH

SDO

Falling SCLK