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When upgrading from MCS® 51 microcontroller to an MCS® 251 microcontroller - is it drop-in compatible?
The MCS 251 is drop-in compatible with the MCS 51 microcontroller, but there are some modifications that need to be considered. Please refer to Application Note AP-710 - Migrating from the MCS 51 Microcontroller to the MCS 251 Microcontroller (8xC251SB). Please note that this document refers to the A-stepping. You must configure the MCS 251 in binary and non-page mode to be compatible with the MCS 51 codes. The recommended configuration bytes are:
UCONFIG0 - 1101 1110B or DEH
UCONFIG1 - 1111 0111B or F7H
You may need to add wait states depending on the speed of the peripheral you are interfacing with.
When upgrading, you will not be able to use the extra address lines in your application. Once you add the extra address lines, the design becomes an MCS 251 design and is no longer considered an MCS 51 upgrade.
What are some considerations for designing microcontroller systems in electrically noisy environments?
Application Note AP-125 - Designing Microcontroller Systems for Electrically Noisy Environments describes some considerations for electrical noise and electrically noisy environments. Some of the discussed design considerations are PCB layout, power supply distribution, and decoupling. In addition, shielding and grounding techniques that may help minimize noise susceptibility are reviewed. Special attention is given to automotive and ESD environments.
Does Intel perform radiation testing on their products?
Radiation testing is not a qualification for Intel parts; therefore, we do not perform radiation testing. However, there are third party test houses that do perform radiation testing on semiconductor devices. These companies can provide more information on their services. Intel does not maintain a list of third party test houses. We recommend searching the Internet for a list of such companies.
Where can I find a description of the MCS 51 Microcontroller Object Module Format?
Download the self-extracting omf51.exe file.
How many interrupt priority levels are there in the MCS 51 microcontroller?
In general, there are 4 interrupt priority levels in each MCS 51 microcontroller. Each interrupt source can be programmed to one of four priority levels, by setting or clearing the bits in the Interrupt Priority and Interrupt Priority High registers. A low-priority interrupt can itself be interrupted by a higher priority interrupt, but not by another interrupt of the same priority. The highest priority interrupt cannot be interrupted by another interrupt source.
If two or more requests of different priority levels are received simultaneously, the request of the higher priority level is serviced. If requests of the same priority level are received simultaneously, an internal polling sequence determines which request is serviced; thus within each priority level there is a second priority structure determined by a polling sequence. The MCS 51 Microcontroller Family User's Manual describes these priorities in greater detail.
How do you access the upper 256 bytes of Expanded RAM (ERAM) in the Expanded RAM series?
When EXTRAM = 0, the 256 bytes of ERAM can be indirectly addressed using the MOVX instruction in combination with any of the R0, R1 registers of the selected bank or the DPTR, an access to ERAM will not affect ports P0, P2, P3.6(WR#) and P3.7(RD#). Address locations 00H - FFH are internal RAM (ERAM). Address locations 100H to FFFFH are external RAM.
The 256 bytes ERAM is physically located on-chip and logically occupies the first 256-bytes of external data memory when the EXTRAM bit is cleared.
How do I set a port pin for a General I/O function?
To use a pin for general-purpose output, set or clear the corresponding bit in the Px register (x = 1, 3 to represent the port#). This should be done each time you require an input from a general-purpose port; although, this is done as default after a valid reset or power up. To use a pin for general-purpose input, set the bit in the Px register. This turns off the output driver FET and allows the port to accept an input. Also, note that the SETB instruction is a read-modify-write function and the contents of the entire port will be read modified and written back into the corresponding port special function register. For more information see the MCS 51 Microcontroller Family User's Manual.
Which MCS 51 microcontrollers have A/D converters?
All members of the 8xC51SL and 8xC51GB families are now End of Life'd (EOL). The 8xC51GB had an 8-channel, 8-bit A/D converter. The 8xC51SL* had a 4-channel, 8-bit A/D converter.
*NOTE: The 8xC51SL was an application specific keyboard controller.
What kind of crystal should I use for the MCS 51 microcontrollers?
Refer to Application Note AP-155 - Oscillators for Microcontrollers. Intel does not "specify" or "recommend" specific off-chip components.
Typically, developers use parallel crystals with 30pF capacitors. However, developers do not have to follow this norm. There are several leniencies and considerations when choosing a crystal. Refer to the Application Note AP-155 and the MCS 51/151/251 Microcontrollers datasheets for issues on specific crystal parameters.
Is there information on changing from Non-FX-Core to FX-Core?
There is information on the differences in core change in the 8XC51FX and 8XC51 Specification Update. Also look at other datasheets for the MCS 51 microcontroller, specifically the 8XC51FX CHMOS Single-Chip 8-Bit Microcontroller Datasheet.
Some of the differences are:
- FX-Core ROM/EPROM Program Lock Differences
- Extended Encryption Array
- Additional Lock Bit
- Modified Quick Pulse
- Additional Signature Byte
- New Mode Pin
- MCS 51 FX QFP Pin 39 Change
- Proper 8xC51FX Encryption Array Usage
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Is there a 16MHz part for the 80C31BH?
You can replace the MCS® 80C31BH with the 87C51. They have the same functionality, except that the 80C31BH is a ROMless and 87C51 has EPROM. When replacing the 80C31BH with an 87C51, tie the EA# pin on the 87C581 to ground. This will enable external memory accessing.
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Intel® MCS® 51 Microcontroller Components
