Mitsubishi Motors DS5000TK - Manual (Page 131)

USER’S GUIDE
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The indeterminate area contains various stacks and
buffers used by the loader, and a given byte in this area
may or may not be modified by the loader. As such the
user should not rely on the bootstrap loader preserving
any data in this area. In a like manner, because not all
locations are used, the indeterminate area of scratch-
pad RAM should not be used for storing security–sensi-
tive data.
The methods of invoking the loader vary between the
DS5000 series and DS5001/DS5002 series, and are
described below.
DS5000 Series
The DS5000 is placed in its Program Load configuration
by simultaneously applying a logic 1 to the RST pin and
forcing the PSEN line to a logic 0 level. Immediately fol-
lowing this action, the DS5000 will look for a serial ASCII
carriage return (0DH) character received at 57600,
19200, 9600, 2400, 1200, or 300 bps over the serial port
or a Parallel Program Load pulse. For whichever type is
first detected, the DS5000 will place itself in the
associated Program Load mode. If an ASCII <CR>
character is detected first, then the DS5000 will place it-
self in the Serial Program Load mode and will ignore any
Parallel Program Strobe pulses. Conversely, if a Paral-
lel Program Strobe pulse is first detected, then the
DS5000 will be placed in the Parallel Program Load
mode and all incoming data on the serial port will be ig-
nored. The selected program load mode will remain in
effect until the next time power is removed from the de-
vice or when the Program Load configuration (RST=1,
PSEN=0) is removed.
In normal programming of the DS5000, problems with
selection of the incorrect Program Load mode will not be
encountered. When the DS5000 is placed in an
8751–compatible programming system, no serial data
will be applied on the RXD pin for the serial port. As a
result, there is almost no chance of random activity on
this pin being interpreted as a <CR> character at a valid
baud rate. Similarly, serial program loading will most
often be performed in the end system. Consequently,
there is again almost no chance of a valid Parallel Pro-
gram Strobe pulse (with V
PP
voltage at 13V) being inter-
preted as a signal to invoke the Parallel Program Load
mode when the Serial Program Load mode is desired.
If the Program Load configuration is removed such that
RST=0 and PSEN=1 with power still applied at V
CC
, the
device will undergo an internal hardware reset and will
begin executing code from the reset vector at 0000h in
Program Memory.
DS5001/DS5002 Series
The DS5001 and DS5002 microcontrollers use an iden-
tical method to invoke the bootstrap loader. A falling
edge on the PROG pin will invoke the loader with a
single device pin. Note that the PROG pin must remain
low for 48 oscillator clocks to be certain of recognition.
Taking the PROG pin to a logic 1 will remove the loader
and cause the DS5001 to perform a reset. Note also that
the PROG pin must be high for as much as 48 clocks
before the CPU is guaranteed to exit the loader. This
constitutes the “pseudo–edge” detection of the program
pin. Note also that pulling RST=1 and PSEN=0 will also
cause the loader to be invoked.
Once the loader mode stimulus has been detected, the
DS5001 will begin looking for an ASCII carriage return
(0Dh). It will look at the serial port and the RPC (8042)
port. For serial reception, the loader will auto–baud at
57600, 19200, 9600, 2400, 1200 and 300 bps. For RPC
mode, the 0Dh value must be written into the Data In
buffer as described in the RPC section under Parallel
I/O. When either of these conditions is detected, the
loader will place itself in that loader mode. Activity on
the other port will be ignored. This condition will remain
until the loader is exited or power is cycled. When the
loader stimulus is removed, the processor will perform a
hardware reset and begin execution at location 0000h.
EXITING THE LOADER
The normal method of leaving the loader is to remove
the stimulus that invoked it. In the DS5000 series, the
RST pin, must be driven low or allowed to float and the
PSEN signal should be allowed to float. The RST pin
has an internal pull–down. The PSEN is an output and
will drive itself. Note that both of these conditions must
occur or the loader will not be exited. For the DS5001,
there are several options. If the RST and PSEN option is
used, the they must be removed as described above. If
PROG is pulled low, it can either be returned high or the
Exit “E” command can be issued. Since the loader is
edge activated, this will restart the user’s code even
while the PROG pin is low. If power were to cycle while
the PROG pin were low, the loader would be invoked on
power up. The flow of these conditions is shown in
Figure 16–1.