Getting Started

[sternter]

Background:

• I have been using the 68HC11 in most all my products since 1990.
• I began using the Cosmic C compiler and Multi-Edit in 1998. 
• In 2003 I incorporated the STMicorelectronics PSD854F2 for all RAM, ROM, addressing logic and some I/O.
• This was a great space saver and I got more memory than with the discretes I had been using.
• Programming was easy: I just used the JTAG port pins and software provided by STMicro
• Now the PSD parts have all gone obsolete.
• This means I must redsign my boards.
• I want to stay with Freescale products
• I want to stay with Cosmic
• I want to upgrade to a more recent and more powerful uProcessor
• I am considering the MC9S12A512 as my replacement device
  • It has plenty of program and storage flash memory onboard
  • It has plenty of I/O
  • It has enough onboard RAM for all my products except one and I can add external RAM for it.
  • An alternative might be the MC9S12XA512.  It has 32K RAM and this would be adequate.
  • You can get an idea of my product line by looking at www.valquest.net

Questions:

1. Does the  MC9S12A512 seem reasonable for my products?
2. Is it reasonable to assume that I can run single chip (no external RAM or ROM)?
3. If so, how do I program it. 
   1. There does not seem to be any JTAG entrance to the chip
   2. I have seen some information about LRAE but I am concerned about:

                                          i.    Programming speed

                                         ii.    What if the LRAE flash area accidentally gets erased?

1. Is there an alternative way to program it?
2. Does Cosmic have any programming tools and/or software for these chips?
3. I see that Cosmic has XGATE development tools.  What exactly is XGATE?
4. Could a MC9S12XA512 help me because of XGATE?

Thanks,

Toby Landes

Valquest Systems, Inc.

[kef]

1. Of course S12A512 will do easily all tasks HC11 is able to do. S12 top bus clock is ~25MHz, and best HC11 IIRC was only 5MHz. S12 code density is better than HC11 code density, so I'm not sure you need 512kB for code space. If you plan to use tens and hundreds kB of data in flash, then I suggest you using something from available S12X families. S12X would greatly improve the speed and lower the overhead of paged data memory accesses (in flash). On S12 paged data memory accesses are way more slower in case your application requires a lot of const data in flash. 16-30kB of data in flash is almost ok, no problem until nonpaged code (ISR's and some runtime routines) plus data fits limited nonpaged flash.  But above that, when you will be forced to move data to paged flash, there will be a lot of overhead sharing single PPAGE register for both, code paging and data paging. S12X is better in this aspect, you have global memory addressing and can read/write all available memory without the need to switch PPAGE register.

2. Single chip design is more robust, less noisy etc. Of course you can run S12 or S12X in single chip mode..

3.1. There's no JTAG on S12(X), but there's single pin BDM interface, which allows to program flash memory and to debug. You need BDM adapter for this. I think most popular is P&E (www.pemicro.com) USB Multilink (USB-ML-12).

3.2  LRAE was to help hobbysts avoid BDM interface expenses, so that they could use RS232 to flash chips. Motorolla/Freescale was going to flash LRAE to every chip at factory programming, but this idea was abandoned many years ago. Additional production operation would mean more costs and more expensive parts. So you have only BDM option.

XGATE is interrupts coprocessor. It's an additional RISC CPU, that can service interrupts and when interrupt servicing is done, XGATE can let main CPU continue interrupt servicing or trigger different CPU interrupt. It can be used for many things. For example SCI ISR handler could collect higher level protocol packet data, validate packet checksum and disturb CPU only when valid packet is received etc. You may check application notes.

You may also look at more fresh (than S12XA) S12XE family. It is faster, contins 12-bits ADC instead of 10-bits ADC available on S12XA etc.