CYW20704
4. Microprocessor Unit
4.1 Overview
The CYW20704 microprocessor unit runs software from the Link Control (LC) layer up to the Host Controller Interface (HCI). The
microprocessor is based on the Cortex-M3 32-bit RISC processor with embedded ICE-RT debug and JTAG interface units. The
microprocessor also includes 848 KB of ROM memory for program storage and boot ROM, 352 KB of RAM for data scratch-pad,
and patch RAM code.
The internal boot ROM provides flexibility during power-on reset to enable the same device to be used in various configurations,
including automatic host transport selection from UART and USB transports with or without external NVRAM. At power-up, the lower
layer protocol stack is executed from the internal ROM.
External patches can be applied to the ROM-based firmware to provide flexibility for bug fixes and features additions. These patches
can be downloaded from the host to the device through the SPI interface or UART and USB transports, or using external NVRAM.
The device can also support the integration of user applications and profiles using an external serial flash memory.
4.2 NVRAM Configuration Data and Storage
4.2.1 Serial Interface
The CYW20704 includes an SPI master controller that can be used to access serial flash memory. The SPI master contains an AHB
slave interface, transmit and receive FIFOs, and the SPI core PHY logic. Data is transferred to and from the module by the system
CPU. DMA operation is not supported.
4.3 EEPROM
The CYW20704 includes a Cypress Serial Control (BSC) master interface. The BSC interface supports low-speed and fast mode
devices and is compatible with I2C slave devices. Multiple I2C master devices and flexible wait state insertion by the master interface
or slave devices are not supported. The CYW20704 provides 400 kHz, full speed clock support.
The BSC interface is programmed by the CPU to generate the following BSC transfer types on the bus:
■ Read-only
■ Write-only
■ Combined read/write
■ Combined write-read
NVRAM may contain configuration information about the customer application, including the following:
■ Fractional-N information
■ BD_ADDR
■ UART baud rate
■ USB enumeration information
■ SDP service record
■ File system information used for code, code patches, or data
4.4 External Reset
The CYW20704 has an integrated power-on reset circuit which completely resets all circuits to a known power on state. This action
can also be driven by an external reset signal, which can be used to externally control the device, forcing it into a power-on reset
state. The RST_N signal is an active-low signal, which is an input to the CYW20704 chip. The CYW20704 does not require an exter-
nal pull-up resistor on the RST_N input.
Document Number: 002-14786 Rev. *E
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