CY7C64601/603/613
2.1
Microprocessor
The CY7C646xx uses a 12-MHz crystal for low EMI. An internal oscillator and PLL develops an internal 48-MHz clock for use by
the USB Serial Interface Engine and the 8051 microprocessor. The 8051 can run at either 24 MHz or 48 MHz, controlled by a
byte in the EEPROM attached to the I
2
C bus. The default rate (with no EEPROM connected) is 24 MHz.
The internal microprocessor is an enhanced version of the industry-standard 8051. Enhancements include 4 clock per cycle
operation, a second data pointer, and an enhanced interrupt system. The 8051 includes two UARTS, three counter-timers, and
256 bytes of register RAM.
The EZ-USB family implements IO differently than the standard 8051, by having its IO control registers in external memory space.
The CY7C646xx preserves this addressing for backward EZ-USB compatibility, and adds the ability to control IO registers using
8051 SFRs (Special Function Registers). This improves IO access time. For example, an IO pin may be toggled using one 8051
instruction, e.g., CPL (bit).
The 8051 program and data memory consists of an internal 8 KB RAM. This RAM is normally downloaded via the USB cable at
plug-in, followed by the 8051 starting up and executing the downloaded code. This gives the CY7C646xx family its ‘soft’ operation
feature, whereby permanent memory such as ROM or Flash memory is not required. Program code updates can easily be done
in the field since the code is loaded from the PC, not by physically changing or reprogramming a memory device. The 8051
program memory can also be loaded from the EEPROM connected to the I
2
C bus on reset for stand-alone use without the USB
connected.
The 128-pin version of the CY7C646xx brings out the full 8051 address and data buses, plus decoded control signals OE#, CS#,
RD#, PSEN, and WR# to allow glueless connection to external memory devices. The 80- and 52-pin packages allow smaller
footprints and more effective solutions for certain designs, but do not have external access to the 8051 buses.
2.2
USB SIE
The CY7C646xx uses the EZ-USB family enhanced SIE (Serial Interface Engine). This SIE has the intelligence to perform full
USB enumeration, creating a default USB device with predefined endpoints and alternate settings. This enhanced SIE is essential
in achieving the family’s soft operation, since it provides the mechanism to download firmware prior to the 8051 running.
Once the 8051 is in control, it can use advanced features of the SIE to simplify its USB firmware. Endpoint zero SETUP data is
placed in a separate 8-byte RAM space for easy access. GET_Descriptor requests are simplified by using a special Setup Data
Pointer. The 8051 simply loads a descriptor address into this 16-bit register, and the SIE takes care of the remaining overhead,
i.e., dividing the descriptor into packets, sending them via endpoint 0 in response to IN tokens, and providing the necessary
handshakes. The 8051 can do other chores while the SIE completes this USB transfer.
Document #: 38-08005 Rev. **
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