Note 1. PC13~PC8: Current Program Counter bits.
2. @7~@0: PCL bits.
3. BP.5: Bank Pointer bit.
4. #12~#0: Instruction code bits.
5. S13~S0: Stack register bits.
6. For the HT48RU80/HT48CU80, the Program Counter is 14 bits wide, i.e. from b13~b0.
7. For the HT48R70A-1/HT48C70-1, since their Program Counter is 13 bits wide, the b13 column
in the table is not applicable.
8. For the HT48R50A-1/HT48C50-1, since their Program Counter is 12 bits wide, the b12 and
b13 columns in the table are not applicable.
9. For the HT48R30A-1/HT48C30-1, since their Program Counter is 11 bits wide, the b11, b12
and b13 columns in the table are not applicable.
10. For the HT48R10A-1/HT48C10-1, since their Program Counter is 10 bits wide, the b10, b11,
b12 and b13 columns in the table are not applicable.
11. The Timer/Event Counter 2 Overflow row is available only for the HT48RU80/HT48CU80.
12. The Timer/Event Counter 1 Overflow row is available only for the HT48R50A-1/HT48C50-1,
HT48R70A-1/HT48C70-1 and HT48RU80/HT48CU80.
13. For the HT48R10A-1/HT48C10-1 and HT48R30A-1/HT48C30-1, the Timer/Event Counter 0
represents the single timer.
14. The UART Bus interrupt is available only for the HT48RU80/HT48CU80 devices.
Stack
This is a special part of the memory which is used to save the contents of the Program Counter
only. The stack can have between 4, 6 or 16 levels depending upon which device is selected and is
neither part of the data nor part of the program space, and is neither readable nor writable. The acti-
vated level is indexed by the Stack Pointer (SP) and is neither readable nor writable. At a subrou-
tine call or interrupt acknowledge signal, the contents of the Program Counter are pushed onto the
stack. At the end of a subroutine or an interrupt routine, signaled by a return instruction (RET or
RETI), the Program Counter is restored to its previous value from the stack. After a chip reset, the
Stack Pointer will point to the top of the stack.
If the stack is full and an enabled interrupt takes place, the interrupt request flag will be recorded
but the acknowledge signal will be inhibited. When the Stack Pointer is decremented (by RET or
RETI), the interrupt will be serviced. This feature prevents stack overflow allowing the program
-
mer to use the structure more easily. However, when the stack is full, a CALL subroutine instruc
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Chapter 1 Hardware Structure
19
P r o g r a m C o u n t e r
S t a c k L e v e l 1
S t a c k L e v e l 2
S t a c k L e v e l 3
S t a c k L e v e l N
P r o g r a m
M e m o r y
T o p o f S T A C K
S t a c k
P o i n t e r
B o t t o m o f S T A C K
B a n k P o i n t e r
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