Rainbow Electronics HT49R70A-1 - Manual (Page 23)

HT49R70A-1
Rev. 1.00 23 December 4, 2001
Low voltage reset/detector functions
There is a low voltage detector (LVD) and a low voltage reset circuit (LVR) implemented in the MCU. These two func-
tions can be enabled/disabled by ROM code options. Once the LVD ROM code options is enabled, the user can use the
RTCC.3 to enable/disable (1/0) the LVD circuit and read the LVD detector status (0/1) from RTCC.5; otherwise, the LVD
function is disabled.
The LVR has the same effect or function with the external RES signal which performs chip reset. During HALT state,
LVR is disabled.
The RTCC register definitions are listed in the table on the next page.
Register Bit No. Label
Read/
Write
Reset Function
RTCC
(09H)
0~2 RT0~RT2 R/W 0
8 to 1 multiplexer control inputs to select the real clock
prescaler output
3 LVDC* R/W 0 LVD enable/disable (1/0)
4 QOSC R/W 0
32768Hz OSC quick start-up oscillating
0/1: quickly/slowly start
5 LVDO R/W 0
LVD detection output (1/0)
1: low voltage detected
6~7 ¾ ¾ ¾ Unused bit, read as ²0²
Note: ²*² Once the LVD function is enabled the reference generator should be enabled; otherwise the reference gen-
erator is controlled by LVR ROM code option. The relationship between LVR and LVD options and LVDC are as
shown.
LVD LVR LVDC V
REF
Generator LVR Comparator LVD Comparator
EN EN ON EN EN EN
EN EN OFF EN EN DIS
EN DIS ON EN DIS EN
EN DIS OFF DIS DIS DIS
DIS EN X EN EN DIS
DIS DIS X DIS DIS DIS
Options
The following shows the mask options in the HT49R70A-1. All these options should be defined in order to ensure
proper functioning system.
Options
OSC type selection. This option is to decide if an RC or crystal or 32768Hz crystal oscillator is chosen as system
clock.
WDT Clock source selection. RTC and Time Base. There are three types of selections: system clock/4 or RTC OSC
or WDT OSC.
WDT enable/disable selection. WDT can be enabled or disabled by option.
CLR WDT times selection. This option defines the method to clear the WDT by instruction. ²One time² means that
the ²CLR WDT² can clear the WDT. ²Two times² means only if both of the ²CLR WDT1² and ²CLR WDT2² have been
executed, the WDT can be cleared.
Time Base time-out period selection. The Time Base time-out period ranges from clock/2
12
to clock/2
15 ²Clock²
means the clock source selected by options.
Buzzer output frequency selection. There are eight types of frequency signals for buzzer output: Clock/2 2 ~Clock/2 9 .
²Clock² means the clock source selected by options.
Wake-up selection. This option defines the wake-up capability. External I/O pins (PA only) all have the capability to
wake-up the chip from a HALT by a falling edge.