欢迎访问ic37.com |
会员登录 免费注册
发布采购

DS1284Q 参数 Datasheet PDF下载

DS1284Q图片预览
型号: DS1284Q
PDF下载: 下载PDF文件 查看货源
内容描述: 看门狗计时器 [Watchdog Timekeepers]
分类和应用: 计时器或实时时钟微控制器和处理器外围集成电路双倍数据速率
文件页数/大小: 18 页 / 384 K
品牌: DALLAS [ DALLAS SEMICONDUCTOR ]
 浏览型号DS1284Q的Datasheet PDF文件第1页浏览型号DS1284Q的Datasheet PDF文件第3页浏览型号DS1284Q的Datasheet PDF文件第4页浏览型号DS1284Q的Datasheet PDF文件第5页浏览型号DS1284Q的Datasheet PDF文件第6页浏览型号DS1284Q的Datasheet PDF文件第7页浏览型号DS1284Q的Datasheet PDF文件第8页浏览型号DS1284Q的Datasheet PDF文件第9页  
DS1284/DS1286  
OPERATION—READ REGISTERS  
The DS1284/DS1286 execute a read cycle whenever WE (write enable) is inactive (high) and CE (chip  
enable) and OE (output enable) are active (low). The unique address specified by the six address inputs  
(A0–A5) defines which of the 64 registers is to be accessed. Valid data is available to the eight data  
output drivers within tACC (access time) after the last address input signal is stable, provided that CE and  
OE access times are also satisfied. If OE and CE access times are not satisfied, then data access must be  
measured from the latter occurring signal (CE or OE) and the limiting parameter is either tCO for CE or tOE  
for OE rather than address access.  
OPERATION—WRITE REGISTERS  
The DS1284/DS1286 are in the write mode whenever the WE and CE signals are in the active-low state  
after the address inputs are stable. The latter occurring falling edge of CE or WE determines the start of  
the write cycle. The write cycle is terminated by the earlier rising edge of CE or WE. All address inputs  
must be kept valid throughout the write cycle. WE must return to the high state for a minimum recovery  
state (tWR) before another cycle can be initiated. Data must be valid on the data bus with sufficient data  
setup (tDS) and data hold time (tDH) with respect to the earlier rising edge of CE or WE. The OE control  
signal should be kept inactive (high) during write cycles to avoid bus contention. However, if the output  
bus has been enabled (CE and OE active), then WE will disable the outputs in tODW from its falling edge.  
DATA RETENTION  
The watchdog timekeeper provides full functional capability when VCC is greater than VTP. Data is  
maintained in the absence of VCC without any additional support circuitry. The DS1284/DS1286  
constantly monitor VCC. Should the supply voltage decay, the watchdog timekeeper automatically write  
protects itself, and all inputs to the registers become “don’t care.” Both INTA and INTB (INTB) are  
open-drain outputs. The two interrupts and the internal clock continue to run regardless of the level of  
VCC. However, it is important to ensure that the pullup resistors used with the interrupt pins are never  
pulled up to a value greater than VCC + 0.3V. As VCC falls below the battery voltage, a power-switching  
circuit turns on the lithium energy source to maintain the clock and timer data functionality. Also ensure  
that during this time (battery-backup mode), the voltage present at INTA and INTB (INTB) never  
exceeds the battery voltage. If the active-high mode is selected for INTB (INTB), this pin only goes high  
in the presence of VCC. During power-up, when VCC rises above approximately 3.0V, the power-switching  
circuit connects external VCC and disconnects the VBAT energy source. Normal operation can resume after  
VCC exceeds VTP for tREC  
.
WATCHDOG TIMEKEEPER REGISTERS  
The watchdog timekeeper has 64 8-bits-wide registers that contain all the timekeeping, alarm, watchdog,  
control, and data information. The clock, calendar, alarm, and watchdog registers are memory locations  
that contain external (user-accessible) and internal copies of the data. The external copies are independent  
of internal functions, except that they are updated periodically by the simultaneous transfer of the  
incremented internal copy (see Figure 1). The command register bits are affected by both internal and  
external functions. This register is discussed later. The 50 bytes of RAM registers can only be accessed  
from the external address and data bus. Registers 0, 1, 2, 4, 6, 8, 9, and A contain time-of-day and date  
information (see Figure 2). Time-of-day information is stored in binary-coded decimal (BCD). Registers  
3, 5, and 7 contain the time-of-day alarm information. Time-of-day alarm information is stored in BCD.  
Register B is the command register and information in this register is binary. Registers C and D are the  
watchdog alarm registers and information stored in these two registers is in BCD. Registers E to 3F are  
user bytes and can be used to contain data at the user’s discretion.  
2 of 18