STV0681 Hardware Interfaces
STV0681
4
STV0681 Hardware Interfaces
4.1
Sensor interface
STV0681 uses a standard ST digital interface from the sensor, and the sensor clock input is
provided by an output from STV0681. The design of a camera using this chipset should be
implemented as closely as possible to the reference design (Chapter 7), in which case the chipset
can be regarded as a functional ‘black box’, and no further details regarding the STV0681-sensor
interface are required.
4.2
Memory interface
STV0681 is designed to interface to an external 16Mbit or 64Mbit SDRAM (see Table 1). The
SDRAM device must have a 16 bit wide data bus and operate from a 3.3V supply. Two sizes of
SDRAM memory are supported by STV0681, 16MBits (1M x 16 bits wide) or 64MBits (4M x 16 bits
wide), the memory size is auto-detected by STV0681. STV0681 clocks the SDRAM at 6MHz,
typically this is well below the figures offered by most manufacturers’ devices.
4.2.1 SDRAM current consumption
For maximum system battery life while no pictures are being taken, and to meet requirements for
USB compliance, an SDRAM should be chosen with the lowest possible self refresh current
specification.
In addition, the USB suspend mode current specification requires that the camera consumes less
than 300µA when un-tethered. Meeting this specification, which is included in the requirements for
USB compliance, assumes an SDRAM with up to approximately 250µA self-refresh current, based
on a current consumption of approximately 50µA for STV0681 + support circuit.
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ADCS 7283313C
STMICROELECTRONICS [ ST ]
