Q
- Why is the MC9S12DG256 the best choice for a low cost trainer or a development
board?
A
- The MC9S12DP256 was the first HCS12 chip that Freescale introduced in 2002 and
has massive on-chip resources in the HCS12 family.
It was the best choice for a trainer, but unfortunately it has been discontinued
by Freescale. The next run-up is the MC9S12DG256 which is cheaper than the
DP512. The DG256 is
identical to the DP256, except it only has 2 CAN ports. Two CAN ports are
more than enough for most applications. Like the DP256, the DG256 has 256K on-chip flash memory, 12K RAM, 4K EEPROM, and up to 91 I/O
lines including 2 SCIs, 3 SPI, I2C, 8 channel 16-bit timers, 2 x 8-ch 10-bit
ADCs, 8-ch, 8-bit or 4-ch, 16-bit PWM, and 5 CANs for all your experiments.
You never know when you will need them in your next application. More I/O pins
are always better! The 12K internal
RAM is large enough for most applications in the classroom environment.
If you move some fully debugged routines to on-chip flash
memory and use RAM for debugging new code, your total program code can larger
than the RAM size. It is faster to
download or modify your code in RAM than in Flash memory. Plus, you also preserve
Flash memory’s life cycle.
Q
- Why should you avoid the MC9S12E128 in your product design as much as
possible?
A - This chip should not be the first choice when selecting one of the HCS12 chips in your product design. The reason is quite simple. The problem of the MC9S12E128 is its uncommon pinouts. Once you design it into your product, you are pretty much locked into this chip. When Freescale chip allocation starts, you cannot replace it with a different HCS12 chip. All other HCS12 chips, except the new C32 family, share the same pinouts and you will have more chances to find a substitute. The advantages of the MC9S12E128 are its low cost and its on-chip DAC. Currently, the new C32 family is even sold at a lower cost. The DAC is seldom used in microcontroller applications. It also can be replaced by a PWM output with a RC integrator or a SPI based DAC, such as the MAX522 or LTC1661.
Q
- Why should you avoid a MC9S12C32 based trainer?
A
- The problem of using the MC9S12C32 on a trainer is its poor on-chip resources.
The C32 family has only one on-chip SCI, and if it’s used for
communicating with the PC during debugging sessions, you do not have another
SCI for your applications. It has much fewer I/O pins than the MC9S12DG256 for your experiments.
The small 32K on-chip flash memory cannot even hold the D-bug12 monitor
because the size of the full-blown D-bug12 monitor is larger than 60K, thus it
will force you to buy a BDM. Purchasing an EVB board that comes
with a BDM at a reasonable price, most likely leaves the student with an
EVB of only limited functionality.
With a BDM, the MC9S12C32 is great for a particular application, like a robot controller, but it is not suitable for a general-purpose trainer or an experimental platform. Our MC9S12C32 based DRAGONfly12 DIP modules are very cheap, but the price should not be the number one factor for deciding which trainer to buy for your students. The performance-to-price ration is the key. Our MiniDRAGON+ and DRAGON12 boards offer much higher performance-to-price ration in a trainer application than the DRAGONfly12 which is not designed be used as a trainer. Our MiniDRAGON+ and the DRAGON12 boards have set a new standard in the "bang for the buck" for the student trainer board market.