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X40030V14-B Datasheet(PDF) 8 Page - Intersil Corporation |
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X40030V14-B Datasheet(HTML) 8 Page - Intersil Corporation |
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8 / 24 page  8 FN8114.1 May 25, 2006 WATCHDOG TIMER The Watchdog Timer circuit monitors the microproces- sor activity by monitoring the SDA and SCL pins. A standard read or write sequence to any slave address byte restarts the watchdog timer and prevents the WDO signal going active. A minimum sequence to reset the watchdog timer requires four microprocessor instructions namely, a Start, Clock Low, Clock High and Stop. The state of two nonvolatile control bits in the Status Register determine the watchdog timer period. The microprocessor can change these watch- dog bits by writing to the X40030, X40031, X40034, X40035 control register (also refer to page 21). Figure 4. Watchdog Restart V1, V2 AND V3 THRESHOLD PROGRAM PROCEDURE (OPTIONAL) The X40030 is shipped with standard V1, V2 and V3 threshold (VTRIP1, VTRIP2, VTRIP3) voltages. These values will not change over normal operating and stor- age conditions. However, in applications where the standard thresholds are not exactly right, or if higher precision is needed in the threshold value, the X40030, X40031, X40034, X40035 trip points may be adjusted. The procedure is described below, and uses the appli- cation of a high voltage control signal. Setting a VTRIPx Voltage (x=1, 2, 3) There are two procedures used to set the threshold voltages (VTRIPx), depending if the threshold voltage to be stored is higher or lower than the present value. For example, if the present VTRIPx is 2.9 V and the new VTRIPx is 3.2 V, the new voltage can be stored directly into the VTRIPx cell. If however, the new setting is to be lower than the present setting, then it is necessary to “reset” the VTRIPx voltage before setting the new value. Setting a Higher VTRIPx Voltage (x=1, 2, 3) To set a VTRIPx threshold to a new voltage which is higher than the present threshold, the user must apply the desired VTRIPx threshold voltage to the corre- sponding input pin (Vcc(V1MON), V2MON or V3MON). Then, a programming voltage (Vp) must be applied to the WDO pin before a START condition is set up on SDA. Next, issue on the SDA pin the Slave Address A0h, followed by the Byte Address 01h for VTRIP1, 09h for VTRIP2, and 0Dh for VTRIP3, and a 00h Data Byte in order to program VTRIPx. The STOP bit following a valid write operation initiates the programming sequence. Pin WDO must then be brought LOW to complete the oper- ation. To check if the VTRIPX has been set, set VXMON to a value slightly greater than VTRIPX (that was previ- ously set). Slowly ramp down VXMON and observe when the corresponding outputs (LOWLINE, V2FAIL and V3FAIL) switch. The voltage at which this occurs is the VTRIPX (actual). CASE A Now if the desired VTRIPX is greater than the VTRIPX (actual), then add the difference between VTRIPX (desired) – VTRIPX (actual) to the original VTRIPX desired. This is your new VTRIPX that should be applied to VXMON and the whole sequence should be repeated again (see Figure 5). CASE B Now if the VTRIPX (actual), is higher than the VTRIPX (desired), perform the reset sequence as described in the next section. The new VTRIPX voltage to be applied to VXMON will now be: VTRIPX (desired) – (VTRIPX (actual) – VTRIPX (desired)). Note: This operation does not corrupt the memory array. Setting a Lower VTRIPx Voltage (x=1, 2, 3) In order to set VTRIPx to a lower voltage than the present value, then VTRIPx must first be “reset” accord- ing to the procedure described below. Once VTRIPx has been “reset”, then VTRIPx can be set to the desired voltage using the procedure described in “Setting a Higher VTRIPx Voltage”. Resetting the VTRIPx Voltage To reset a VTRIPx voltage, apply the programming volt- age (Vp) to the WDO pin before a START condition is set up on SDA. Next, issue on the SDA pin the Slave Address A0h followed by the Byte Address 03h for VTRIP1, 0Bh for VTRIP2, and 0Fh for VTRIP3, followed by 00h for the Data Byte in order to reset VTRIPx. The STOP bit following a valid write operation initiates the programming sequence. Pin WDO must then be brought LOW to complete the operation. After being reset, the value of VTRIPx becomes a nomi- nal value of 1.7V or lesser. Notes: 1.This operation does not corrupt the memory array. 2. Set VCC ≅ 1.5(V2MON or V3MON), when setting VTRIP2 or VTRIP3 respectively SCL SDA .6µs 1.3µs WDT Reset Start Stop X40030, X40031, X40034, X40035 |
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