Errata
•
•
•
•
•
•
•
•
•
•
•
LDS/STS when Accessing External RAM
STS when Accessing EEPROM
COM1B Settings Never Disconnects OC1B
UART Loses Synchronization if RXD Line is Low when UART Receive is Disabled
Releasing Reset Condition without Clock
Lock Bits at High V
CC
The SPI Can Send Wrong Byte
Reset during EEPROM Write
SPI Interrupt Flag Can be Undefined after Reset
Serial Programming at Voltages below 3.0 Volts
Skip Instructions with Interrupts
11. LDS/STS when Accessing External RAM
Using an LDS instruction for reading external RAM corrupts the source register
used in the LDS instruction when directly followed by NOP. An STS instruction for
writing to external RAM corrupts R0 when directly followed by NOP.
Problem Fix/Workaround
Do not insert a NOP instruction directly after an LDS or STS instruction used for
accessing the external RAM.
10. STS when Accessing EEPROM
If the STS instruction is used to start an EEPROM write (EEWE in EECR), the
following instruction may have an undesired result. In the case of NOP, R0
will be corrupted.
Problem Fix/Workaround
Use the OUT or SBI instruction to start an EEPROM write.
9. COM1B Settings Never Disconnects OC1B
According to the datasheet, Timer/Counter1 should be disconnected from the
OC1B pin when COM1B[1:0] = “00” in non-PWM mode, and when
COM1B[1:0] = “00” or “01” in PWM mode. This, however, is not the case.
For OC1A, the description in the datasheet is correct; the general digital I/O func-
tion takes over.
Problem Fix/Workaround
As OC1B is an output only pin with no general digital I/O function, the pin cannot
be tri-staded. However, if there is a need to stop the pin from toggling, disable the
PWM mode by setting PWM[1:0] to “00” and set the COM1A[1:0] to anything else
than “01” (which is the toggle mode). Warning: As long as the timer is still running,
the counter can count to a value above the maximum for that PWM mode. As an
alternative, the timer can be stopped by setting CS1[2:0] in TCCR1B to “000”.
8. UART Loses Synchronization if RXD Line is Low when UART Receive is
Disabled
The UART will detect an UART start bit and start reception even if the UART is not
enabled. If this occurs, the first byte after reenabling the UART will be corrupted.
Problem Fix/Workaround
Make sure that the RX line is high at start-up and when the UART is disabled. An
external RS232-level converter keeps the line high during start-up.
8-bit
Microcontroller
with 8K Bytes
In-System
Programmable
Flash
AT90S8515
Rev. B
Errata Sheet
Rev. 1195E–09/01
1
7.
Releasing Reset Condition without Clock
If an external reset or a watchdog reset occurs while the clock is stopped and the reset is released before the clock is
restarted, the internal reset will time-out after the start-up delay which is independent of the external clock. If no exter-
nal clock pulses are present in the period when internal reset is active, the reset does correctly cause tristating of the
I/O while the reset is held. However, if the internal reset is released before the clock starts running, the part does not
clear I/O registers, nor set PC to 0x00. Here, stopping the clock refers to gating the external clock input. Power Down
mode does not have this issue.
Problem Fix/Workaround
Make sure the clock is running whenever an external reset can be expected. If the Watchdog is used, never stop an
external clock.
6. Lock Bits at High V
CC
On some devices, the lock bits will not erase at high V
CC
and temperature. In this situation, it will not be possible to
reprogram the devices when the lock bits are set. This errata strongly depends on temperature and should in most
cases not cause any problems at room temperature.
Problem Fix/Workaround
Lower V
CC
below 4.0V before performing a chip erase. Then the device will unlock at any temperature and it will be
possible to reprogram the device at any V
CC
.
Use rev. C or higher.
5. The SPI can Send Wrong Byte
If the SPI is in Master mode, it will restart the old transfer if new data is written on the same clock edge as the previous
transfer is finished.
Problem Fix/Workaround
When writing to the SPI, first wait until it is ready; then write the byte to transmit.
4. Reset during EEPROM Write
If reset is activated during EEPROM write, the result is not what should be expected. The EEPROM write cycle com-
pletes as normal, but the address registers are reset to 0. The result is that both the address written and address 0 in
the EEPROM can be corrupted.
Problem Fix/Workaround
Avoid using address 0 for storage, unless you can guarantee that you will not get a reset during EEPROM write.
3. SPI Interrupt Flag can be Undefined after Reset
In certain cases when there are transitions on the SCK pin during reset, or the SCK pin is left unconnected, the start-up
value of the SPI interrupt flag is unknown. If the flag is not reset before enabling the SPI interrupt, a pending SPI inter-
rupt may be executed.
Problem Fix/Workaround
Clear the SPI interrupt flag before enabling the interrupt.
2. Serial Programming at Voltages below 3.0 Volts
At voltages below 3.0 volts, serial programming might fail.
Problem Fix/Workaround
Keep V
CC
at 3.0 volts or higher during In-System Programming.
2
AT90S8515 Errata
1195E–09/01
AT90S8515 Errata
1. Skip Instruction with Interrupts
A skip instruction (SBRS, SBRC, SBIS, SBIC, CPSE) that skips a 2-word instruction needs 3 clock cycles. If an inter-
rupt occurs during the first or second clock cycle of this skip instruction, the return address will not be stored correctly
on the stack. In this situation, the address of the second word in the 2-word instruction is stored. This means that on
return from interrupt, the second word of the 2-word command will be decoded and executed as an instruction. The
AT90S8515 has two 2-word instructions: LDS and STS.
Note 1: This can only occur if all of the following conditions are true:
- A skip instruction is followed by a 2-word instruction.
- The skip instruction is actually skipping the 2-word instruction.
- Interrupts are enabled, and at least one interrupt source can generate an interrupt.
- An interrupt arrives in the first or second cycle of the skip instruction.
Note 2: This will cause problems only if the address of the following LDS or STS command points to an address
beyond 400 Hex.
Problem Fix/Workaround
For assembly program, avoid skipping a 2-word instruction if interrupts are enabled.
The following C-compilers handle this sequence correctly:
- IAR Compiler, version 1.40b or later
- Image Craft Compiler, all versions
- Codevision Compiler, version 1.0.0.5 or later
3
1195E–09/01
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