HT36A1 Holtek Semiconductor Inc., HT36A1 Datasheet - Page 6

• Manufacturer Part Number: HT36A1
• Description: Ht36a1 -- Music Synthesizer 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

Function Description
Execution Flow
The system clock for the HT36A1 is derived from either
a crystal or an RC oscillator. The oscillator frequency di-
vided by 2 is the system clock for the MCU
(f
non-overlapping clocks. One instruction cycle consists
of four system clock cycles.
Instruction fetching and execution are pipelined in such
a way that a fetch takes one instruction cycle while de-
coding and execution takes the next instruction cycle.
However, the pipelining scheme causes each instruc-
tion to effectively execute in one cycle. If an instruction
changes the program counter, two cycles are required
to complete the instruction.
Program Counter - PC
The 13-bit program counter (PC) controls the sequence
in which the instructions stored in program ROM are ex-
ecuted and its contents specify a maximum of 8192 ad-
dresses for each bank.
After accessing a program memory word to fetch an in-
struction code, the contents of the program counter are
incremented by one. The program counter then points to
the memory word containing the next instruction code.
Note:
Rev. 1.10
Initial Reset
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
Skip
Loading PCL
Jump, Call Branch
Return From Subroutine
OSC
=f
SYS
*12~*0: Bits of Program Counter
#12~#0: Bits of Instruction Code
@7~@0: Bits of PCL
2) and it is internally divided into four
Mode
PF2 PF1 PF0 *12 *11 *10 *9
PF2 PF1 PF0 #12 #11 #10 #9
PF2 PF1 PF0 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 S0
*15 *14 *13 *12 *11 *10 *9
0
0
0
0
0
0
0
0
0
Program Counter
Execution Flow
0
0
0
0
0
0
6
When executing a jump instruction, conditional skip ex-
ecution, loading PCL register, subroutine call, initial re-
set, internal interrupt, external interrupt or return from
subroutine, the PC manipulates the program transfer by
loading the address corresponding to each instruction.
The conditional skip is activated by instruction. Once the
condition is met, the next instruction, fetched during the
current instruction execution, is discarded and a dummy
cycle replaces it to retrieve the proper instruction. Other-
wise proceed with the next instruction.
The lower byte of the program counter (PCL) is a read-
able and writeable register (06H). Moving data into the
PCL performs a short jump. The destination will be
within 256 locations.
Once a control transfer takes place, an additional
dummy cycle is required.
Program ROM
HT36A1 provides 16 address lines WA15~0 to read the
Program ROM which is up to 1M bits, and is commonly
used for the wavetable voice codes and the program
memory. It provides two address types, one type is for
program ROM, which is addressed by a bank pointer
PF2~0 and a 13-bit program counter PC12~0; and the
@7~@0: Bits of PCL
S12~S0: Bits of Stack Register
PF2~PF0: Bits of Bank Register
0
0
0
Program Counter+2
Program Counter
0
0
0
#8
*8
*8 @7 @6 @5 @4 @3 @2 @1 @0
0
0
0
#7
*7
0
0
0
#6
*6
0
0
0
#5
*5
0
0
0
#4
*4
0
0
0
#3
*3
0
1
1
March 12, 2007
#2
*2
0
0
1
HT36A1
#1
*1
0
0
0
#0
*0
0
0
0