20-668-0003 Rabbit Semiconductor, 20-668-0003 Datasheet - Page 219

• Manufacturer Part Number: 20-668-0003
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0003

• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 30 MHz
• Operating Supply Voltage: 0 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 40
• Number Of Timers: 8 & 10 bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 20-668-0003; 316-1062

B.2.6 Write Inhibit (/WE0) After Reset
This feature, available in revisions A–C, modified the reset state of the MB0CR register to
inhibit /WE0. Inhibiting writes after reset prevents the processor from inadvertently writ-
ing to an unprogrammed flash memory that doesn’t have the software data protection
enabled. In a flash memory where the software data protection is enabled, an inadvertent
write will temporarily disable the flash memory if the memory is used to execute code.
This has not been a serious problem in the past for two reasons. First, programming sys-
tems using Dynamic C permanently enable software data protection, and second, most
manufacturers ship their memory devices with software data protection permanently
enabled.
Software data protection consists of a three-byte load sequence that is used to initiate pro-
gram operation during the system power-up or power-down, providing protection from
inadvertent write operations. Flash devices usually provide a chip-erase operation, which
allows the user to erase the entire memory array to the ‘1’s state. Flash devices are nor-
mally erased prior to shipment. When the Rabbit processor comes out of reset, it begins
fetching instructions from address zero of the device connected to /CS0, /OE0, and /WE0,
which in most cases is a flash memory. If the flash contains 0xff at address zero, the pro-
cessor will decode this as an RST 38. An RST 38 vectors to an ISR area at address 0x70
and pushes the PC onto the stack, which by default is located at address 0x00 (flash mem-
ory). This can be a problem if the flash is repeatedly written to in an endless loop because
flash memories can only endure a finite number of writes, typically about 100,000.
B.2.7 Chip Selects Inactive During Internal I/O
In the original Rabbit 2000, it was found that whichever chip select was mapped to
MB0CR would become active during internal I/O operations. This behavior did not cause
any problems, but was corrected in revisions A–C.
B.2.8 External Interrupt Input Bug Fix
The external interrupt bug discovered in the original Rabbit 2000 required the external
interrupt inputs to be tied together with a resistor as described in Technical Note TN301,
Rabbit 2000 Microprocessor Interrupt Problem. This bug was subsequently fixed in revi-
sions A-C of the Rabbit 2000, and two separate external interrupt inputs are available on
these devices.
B.2.9 IOI/IOE Prefix Bug Fix
Certain instructions did not function correctly as described in Technical Note TN302,
Rabbit 2000 Instruction Bug. The problem was corrected in revisions A–C of the Rabbit
2000.
Appendix B Rabbit 2000 Revisions
213