SyncMOS Technologies International, Inc.
SM5964A
8-Bit Micro-controller
With 64KB ISP Flash & TWSI & PWM & 1KB RAM embedded
PHASE
OSC
P1
P2
P1
P2
P1
P2
P1
P2
P1
P2
P1
P2
P1
P2
P1
(Xtal2)
SEQUENCE
S1
S2
S3
S4
S5
S6
S1
S2
Figure 13 Sequences and Phases
FIGURE 14 shows the fetch / execute sequences in states and phases for various kinds of instructions. Normally the
program fetches are generated during each machine cycle, even if the instruction being executed doesn’t require it. If the
instruction being executed doesn’t need more code bytes, the CPU simply ignores the extra fetch, and the PROGRAM
COUNTER is incremented accordingly.
Execution of a one-cycle instruction (FIGURE 14 A and B) begins during S1 of the machine cycle, when the OPCODE is
latched into INSTRUCTION REGISTER. A second fetch occurs during S4 of the same machine cycle. Execution is
completed at the end of S6 of this machine cycle.
The MOVX instructions take two machine cycles to execute. No program fetch is generated during the second cycle of a
MOVX instruction. This is the only time program fetches are skipped. The fetch/execute sequence for MOVX instructions
is shown in FIGURE 14 (D)
The fetch / execute sequences are the same whether the PROGRAM MEMORY is internal or external to the chip.
Execution times do not depend on whether the PROGRAM MEMORY is internal or external.
FIGURE 15 shows the signals and timing involved in program fetches when the program memory is external. If
PROGRAM MEMORY is external, the PROGRAM MEMORY READ STOBE (/PSEN) is normally activated twice per
machine cycle, as shown in FIGURE 15(A).
If an access external DATA MEMORY occurs, as shown in FIGURE 15(B), two (/PSEN) are SKIPPED, because the
address and data bus are being used for DATA MEMORY access.
Note that a DATA MEMORY bus cycle takes twice as much time as PROGRAM MEMORY bus cycle. FIGURE 15
shows the relative time of the address begin emitted at PORT0 and PORT2, and of ALE and /PSEN. ALE is used to latch
the low address byte form PORT0 into the address latch.
When CPU is executing from internal PROGRAM MEMORY, /PSEN is not activated, and program address are not
emitted. However, ALE continues to be activated twice per machine cycle and so is available as clock output signal. Note,
however, that ALE is skipped during the execution of the MOVX instruction.
Specifications subject to change without notice contact your sales representatives for the most recent information.
Ver 2.3 SM5964A 10/2006
14
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
