Chapter 2 Devices 2.2.16 Additional Remarks on Special Auxiliary Relays and Special Data Registers 1. The scan timeout timer SM8/SR8 When a scan timeout occurs during the execution of the program, the error LED indicator on the PLC is ON all the time, and SM8 is ON. The content of SR8 is the step address at which the watchdog timer is ON. 2. Clearing the warning light SM22 If SM22 is ON, the error log and the warning light will be cleared. 3. The real-time clock SM220, SR220~SR226, and SR391~SR397 SM220: Calibrating the real-time clock within ±30 seconds When SM220 is switched from OFF to ON, the real-time clock is calibrated.
If the value of the second in the real-time clock is within the range between 0 and 29, the value of the minute is fixed, and the value of the second is cleared to zero. If the value of the second in the real-time clock is within the range between 30 and 59, the value of the minute increases by one, and the value of the second is cleared to zero. The corresponding functions and values of SR220~SR226 and SR391~SR397 are as follows. SR391~SR397 correspond to SR220~ SR226. The difference between SR220~ SR226 and SR391~SR397 lies in the fact that the former adopts the binary-coded decimal while the latter adopts the decimal system.
For example, December is represented as 12 in SR392 while it is represented as 12 in the binary-coded decimal. 2-75 Special data register Refresh time SR1270~SR1279 The register is refreshed when the parameter is downloaded to the PLC. SR1280~SR1281 The register is refreshed when the parameter is downloaded to the PLC, or when the PLC is supplied with power. SR1282~SR1291 The register is refreshed when the parameter is downloaded to the PLC. SR1292~SR1293 The register is refreshed when the parameter is downloaded to the PLC, or when the PLC is supplied with power. SR1294~SR1303 The register is refreshed when the parameter is downloaded to the PLC.
SR1304~SR1305 The register is refreshed when the parameter is downloaded to the PLC, or when the PLC is supplied with power. SR1306~SR1315 The register is refreshed when the parameter is downloaded to the PLC. SR1316~SR1320 The register is refreshed when the parameter is downloaded to the PLC, or when the PLC is supplied with power. SR1329~SR1334 Users set the value and clear it. SR1335~SR1336 The register is refreshed every scan cycle when the PLC Link is enabled. SR1337~SR1787 Users set the value and clear it. SR1792~SR2047 The register is refreshed every scan cycle.
Device Binary-coded Decimal Function Value decimal system system SR220 SR391 Year 00~99 (A.D.) SR221 SR392 Month 1~12 SR222 SR393 Day 1~31 SR223 SR394 Hour 0~23 SR224 SR395 Minute 0~59 SR225 SR396 Second 0~59 SR226 SR397 Week 1~7