MC68HC05B6_13 Datasheet, PDF (176/302 Pages) Freescale Semiconductor, Inc – Microcontrollers

Table C-3 Bootstrap vector targets in RAM
Vector targets in RAM
SCI interrupt
Timer overflow
Timer output compare
Timer input capture
IRQ
SWI
$00E4
$00E7
$00EA
$00ED
$00F0
$00F3
A 10-byte stack is also reserved at the top of the RAM allowing, for example, one interrupt and two
sub-routine levels.
Program execution is triggered by sending a negative (bit 7 set) high address; execution starts at
address XADR ($0083).
The RAM addresses between $0050 and $0082 are used by the loader and are therefore not
available to the user during serial loading/executing.
Refer to Figure C-7 shows a suitable circuit. Figure C-9 shows address and data bus timing.
C.5.4 RAM parallel bootstrap load and execute
The RAM bootstrap program will start loading the RAM with external data (e.g. from a 2564 or
2764 EPROM). Before loading a new byte, the state of the PD4/AN4 pin is checked; if this pin goes
to level ‘0’, or if the RAM is full, then control is given to the loaded program at address $0050.
If the data is supplied by a parallel interface, handshaking will be provided by PC5 and PC6
according to Figure C-10. If the data comes from an external EPROM, the handshake can be
disabled by connecting together PC5 and PC6.
Figure C-8 shows a circuit that can be used to load the RAM with short test programs. Up to 8
programs can be loaded in turn from the EPROM. Selection is accomplished by means of the
switches connected to the EPROM higher address lines (A8 through A10). If the user program sets
PC0 to level ‘1’, the external EPROM will be disabled, rendering both port A outputs and port B
inputs available.
The EPROM parallel bootstrap loader circuit (Figure C-6) can also be used, provided VPP is tied
to V_DD. The high order address lines will be at zero. The LEDs will stay off.
14
Freescale
C-14
MC68HC705B5
MC68HC05B6
Rev. 4.1