Bit Parity
Bit Parity
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Decoding the DCF-77 Radio Time Signal
The DCF-77 radio time transmission is utilised by many NTP server and PC computer systems to provide accurate synchronisation of time critical applications. This article describes how the DCF-77 time signal is decoded by NTP server and computer systems to provide an accurate timing reference.
The DCF-77 Time Transmitter.
The DCF-77 time signal is a long-wave radio time signal broadcast from Mainflingen, near Frankfurt, Germany. The radio signal is maintained by T-Systems, a sub-division of Deuche Telecom, and has been in operation since 1959. The DCF-77 signal is generated from extremely accurate atomic clocks located at the German National Physics Laboratory. When decoded, it provides a highly accurate timing reference for clocks and computer timing equipment.
DCF-77 Time Code.
Time and date information is transmitted continuously, repeated each minute. The data is transmitted as an amplitude modulated, pulse-width coded data signal. Each data bit is transmitted as one pulse per second. The data transmitted consists of the current time and date, leap second indicator, daylight saving time indicator, transmitter identifier and parity bits.
The duration of each transmitted pulse is decoded as follows: a second mark with a duration of 100 milliseconds is decoded as a binary zero; a second mark with a duration of 200 milliseconds is decoded as a binary one.
Transmitted Data.
Time and date information is presented in BCD (Binary Coded Decimal) format and is encoded as follows: bits 0-14 are unused, but may provide future status information; bit 15 indicates use of backup transmitter; bit 16 (A1), indicates the announcement of daylight saving change; bit 17 (Z1), indicates daylight saving is in use (CEST); bit 18 (Z2), indicates standard time (CET); bit 19 (A2), announces a leap second; bit 20, indicates start of time information; bits 21-27, BCD encoded minutes; bit 28 (P1), parity bit covers bits 21-27; bits 29-34, BDC encoded hours; bit 35 (P2), parity bit covers bits 29-34; bits 36-41, BCD encoded day of month; bits 42-44, BCD encoded day of week; bits 45-49, BCD encoded month of the year; bits 50-57, BCD encoded year; bit 58 (P3), parity bit covers bits 36-57.
The DCF-77 data bits 1-14 are generally unused by any decoding algorithm and may provide status information in future broadcasts. The time zone bits Z1 and Z2 indicate current daylight saving time status. When CET time is being broadcast, Z1 is zero and Z2 is one, for CEST time, Z1 is one and Z2 is zero. The daylight saving change announcement bit, A1, indicates an imminent change to or from CET. The leap second announcement bit indicates the imminent insertion of a leap second. The three parity bits P1-P3 compliment the preceding information to an even number of ones (even parity).
Examples:
Received DCF-77 bit stream: 00000000000000000010100000000011010110000001001001000110011 Decoded time and date: Tuesday 01/12/1998 16:00
Received DCF-77 bit stream: 00000000000000000010110000001011010110000001001001000110011 Decoded time and date: Tuesday 01/12/1998 16:01Dave Evans develops NTP Server synchronisation systems to ensure accurate time on PC's and computer networks. Dave has been involved in the development of dedicated NTP server systems, NTP synchronised digital wall clock systems and atomic clock time synchronisation products. Click here to find out more about SNTP and DCF-77NTP ServerSystems.
Article Source: http://www.simplysearch4it.com/article/50512.html
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8-N-1 $62.4 Used - High Quality Content by WIKIPEDIA articles! 8-N-1 is a common shorthand notation for a serial port parameter setting or configuration in asynchronous mode, in which there are eight (8) data bits, no (N) parity bit, and one (1) stop bit. 8-N-1 is the most common configuration for PC serial communications today. The abbreviation is usually given together with the line speed in bits per second, as in 9600/8-N-1. The speed includes bits for framing (stop bits, parity, etc.) and the effective |
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8x2 (8:2) Multi-Video HDMI Composite S-Video Component VGA Video + Audio Converter & Matrix Switcher $1292 The SB-3877 is a Multi-Video switcher featuring 8 inputs and 2 outputs (independent of each other) making this a true Matrix Routing Switcher. The Inputs are comprised of: 2 HDMI, 2 Composite Video w/Audio, 2 S-Video w/Audio, 2 Component video w/Audio, and 2 VGA w/Audio. The Outputs are 2 HDMI w/Digital Audio and 2 VGA w/Audio. Note that you can use BOTH the VGA Output and the HDMI Output simultaneously giving you 2 outputs per channel for a total of 4 outputs per chassis. Formats supported are NTSC/PAL/SECAM video system. Supports High Definition Digital signal with data rates enabling 1080i formats or if in PC resolution (1920x1200). It completely eliminates the need to constantly move around HD input and output cables. Control is provided via Front push buttons with LED readout or IR remote controller. A RS-232 interface is provided for interfacing with third party control or use the provided software. Input cable equalizer enables use of long cable runs of more than 50 feet (15 meters) when using 24 AWG cable at 1080i. A windows-based control software package is included to provide complete control of the SB-3866 from a PC. TECHNICAL SPECIFICATIONS: **Auto Detection TV Video System: NTSC-M 3.58, NTSC-J, 4.43, PAL-B-D-I-G-H-K, PAL-M, PAL-N, PAL-N COMB-N, SECAM (Impedance:75 ohms). **SD Menu Selections: Adjust Color, Contrast, Brightness, Sharpness, Level and Gain. **Video Bandwidth: 250MHz, (-3 dB). **Audio Bandwidth: 60MHz, (-3 dB). **Audio Frequency Response: 20Hz ~ 20KHz. **Input Source Resolutions: HDMI = 480p, 720p & 1080p, Component Video (YPBPR) = 480p, 720p & 1080p, PC = VGA (640x480), SVGA (800x600), XGA (1024x768), SXGA (1280x1024). **Maximum Unit Output Resolutions: HDMI = 720p & 1080p, VGA = SVGA (800x600), XGA (1024x768), SXGA (1280x1024), WXGA (1366x768) WXGA+ (1680x1050), WUXGA (1920x1200). **Weight: 3.5 Kgs. **Control: Direct Front Panel menu, Remote control & RS-232/RS-485. **Rs232 Control: 9600 bps, No Parity, 8 bits, 1 Stop bit. **Safety Approv |