參數(shù)資料
型號: TDA935X
廠商: NXP Semiconductors N.V.
英文描述: TV signal processor-Teletext decoder with embedded m-Controller
中文描述: 電視信號處理器與嵌入式米圖文電視解碼器控制器
文件頁數(shù): 36/140頁
文件大小: 570K
代理商: TDA935X
Philips Semiconductors
Preliminary specification
1999 Sep 28
36
TV signal processor-Teletext decoder with
embedded
μ
-Controller
TDA 935X/6X/8X series
TCON, TMOD, TL0, TH0, TL1 and TH1.
The Timer/Counter function is selected by control bits C/T in the Timer Mode SFR(TMOD). These two Timer/
Counter have four operating modes, which are selected by bit-pairs (M1.M0) in the TMOD. Details of the modes
of operation are given in the "80C51 Based 8-Bit Microcontrollers - Philips Semiconductors (ref. IC20)"
(Reference [1]).
TL0 and TH0 are the actual timer/counter registers for timer 0. TL0 is the low byte and TH0 is the high byte. TL1
and TH1 are the actual timer/counter registers for timer 1. TL1 is the low byte and TH1 is the high byte.
WatchDog Timer
The WatchDog timer is a counter that when it overflows forces the microcontroller in to a reset. The purpose of
the WatchDog timer is to reset the microcontroller if it enters an erroneous processor state (possibly caused by
electrical noise or RFI) within a reasonable period of time. When enabled, the WatchDog circuitry will generate
a system reset if the user program fails to reload the WatchDog timer within a specified length of time known as
the WatchDog interval.
The WatchDog timer consists of an 8-bit counter with an 11 bit prescaler. The prescaler is fed with a signal
whose frequency is 1/12 fosc (1MHz). The 8 bit timer is incremented every ‘t’ seconds where:
t=12x2048x1/fosc=12x2048x1/12x10
6
= 2.048ms
W
ATCH
D
OG
T
IMER OPERATION
The WatchDog operation is activated when the WLE bit in the Power Control SFR (PCON) is set. The WatchDog
can be disabled by Software by loading the value 55H into the WatchDog Key SFR (WDTKEY). This must be
performed before entering Idle/Power Down mode to prevent exiting the mode prematurely.
Once activated the WatchDog timer SFR (WDT) must be reloaded before the timer overflows. The WLE bit must
be set to enable loading of the WDT SFR, once loaded the WLE bit is reset by hardware, this is to prevent
erroneous Software from loading the WDT SFR.
The value loaded into the WDT defines the WatchDog interval.
WatchDog interval = (256 - WDT) * t = (256 -WDT)*2.048ms
The range of intervals is from WDT = 00H which gives 524ms to WDT = FFH which gives 2.048ms
PORT Alternate Functions
The Ports 1,2 and 3 are shared with alternate functions to enable control of external devices and circuitry. The
alternate functions are enabled by setting the appropriate SFR and also writing a logic ‘1’ to the Port bit that the
function occupies.
If the Pulse Width Modulator outputs (PWM) are required on Ports 3.0 to 3.3, they require an additional bit to be
set in the Character ROM. If this facility is required, it should be requested when ordering the Language Set.
The PWMs may be enabled per pin, thus giving any combination of either PWM output, SFR output or SAD
input.
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