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Z8 Microcontrollers
Power-Down Modes
ZiLOG
UM001600-Z8X0599
8-3
8.4 STOP-MODE RECOVERY REGISTER
This register selects the clock divide value and determines
the mode of STOP-Mode Recovery (Figure 8-1). All bits
are Write-Only, except bit 7, that is Read-Only. Bit 7 is a
flag bit that is hardware set on the condition of STOP re-
covery and reset by a power-on cycle. Bit 6 controls wheth-
er a low level or a high level is required from the recovery
source. Bit 5 controls the reset delay after recovery. Bits 2,
3, and 4, of the SMR register, specify the source of the
STOP-Mode Recovery signal. Bits 0 and 1 control internal
clock divider circuitry. The SMR is located in Bank F of the
Expanded Register File at address 0BH.
Note:
The SMR register is available in select Z8 MCU products. Refer to the device product specification to determine
SMR options available.
SCLK/TCLK Divide-by-16 Select (DO).
This bit of
the SMR controls a divide-by-16 prescaler of SCLK/TCLK.
The purpose of this control is to selectively reduce device
power consumption during normal processor execution
(SCLK control) and/or HALT mode (where TCLK sources
counter/timers and interrupt logic).
External Clock Divide-by-Two (D1).
This bit can
eliminate the oscillator divide-by-two circuitry. When this
bit is 0, the System Clock (SCLK) and Timer Clock (TCLK)
are equal to the external clock frequency divided by two.
The SCLK/TCLK is equal to the external clock frequency
when this bit is set (D1=1). Using this bit together with D7
of PCON helps further lower EMI (D7 (PCON) =0, D1
(SMR) =1). The default setting is zero.
Figure 8-1. STOP-Mode Recovery Register
(Write-Only Except Bit D7, Which Is Read-Only)
D7 D6 D5 D4 D3 D2 D1 D0
SMR (FH) 0B
STOP-Mode Recovery Source
000 POR Only and/or External Reset
001 P30
010 P31
011 P32
100 P33
101 P27
110 P2 NOR 0-3
111 P2 NOR 0-7
0 OFF **
1 ON
SCLK/TCLK Divide-by-16
0 OFF
1 ON*
Stop Delay
0 POR*
1 Stop Recovery
Stop Flag (Read Only)
External Clock Divide by 2
1 SCLK/TCLK = XTAL
0 Low*
1 High
Stop Recovery Level
* Default setting after RESET.
** Default setting after RESET and STOP-Mode Recovery.