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TC520 Datenblatt(PDF) 6 Page - Microchip Technology |
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TC520 Datenblatt(HTML) 6 Page - Microchip Technology |
6 / 16 page TC520A DS21431B-page 6 © 2002 Microchip Technology Inc. 3.0 DETAILED DESCRIPTION 3.1 TC520A Timing The TC520A consists of a serial port and state machine. The state machine provides control timing to the TC5xx A/D converter connected to the TC520A as well as providing sequential timing for TC520A internal operation. All timing is derived from the frequency source at OSCIN and OSCOUT. This frequency source can be either an externally provided clock signal or external crystal. If an external clock is used, it must be connected to the OSCIN pin and OSCOUT must remain floating. If a crystal is used, it must be connected between the OSCIN and OSCOUT and be physically located as close to the OSCIN and OSCOUT pins as possible. The incoming frequency is internally divided by 4 and the resulting clock (SYSCLK) controls all timing functions. 3.2 TC5XX A/D Converter Control Signals The TC520A control outputs (A, B) and control input (CMPTR) connect directly to the corresponding pins of the TC5XX A/D converter. A conversion is consum- mated when A, B have been sequenced through the required 4 phases of conversion: Auto Zero (AZ), Inte- grate (INT), De-integrate (DINT) and Integrator Zero (IZ) (see Figure 4-1). The Auto Zero phase compensates for offset errors in the TC5XX A/D converter. The Integrate phase connects the voltage to be converted to the TC5XX A/D converter input, resulting in an inte- grator output dv/dt directly proportional to the magni- tude of the applied input voltage. Actual A/D conversion (counting) is initiated at the start of the DINT phase and terminates when the integrator output crosses 0V. The integrator output is then forced to 0V during the IZ phase and the converter is ready for another cycle. Please see the TC500/TC500A/TC510/TC514 data sheet for a complete description of these phases. The number of SYSCLK periods (counts) for the AZ and INT phases is determined by the LOAD VALUE. The LOAD VALUE is a single byte that must be loaded into the most significant byte of 16-bit counter on board the TC520A during initialization. The lower byte of this counter is pre-loaded to a value of 0FFH (25610)and cannot be changed. The LOAD VALUE (upper 8 bits of the counter) can be programmed over a range of 0FFH to 00H (corre- sponding to a range of AZ = INT = 256 counts to 65536 counts). (See Figure 3-2). The LOAD VALUE sets the number of counts for both the AZ and INT phases and directly affects resolution and speed of conversion. The greater the number of counts allowed for AZ and INT, the greater the A/D resolution (but the slower the con- version speed). The time period required for the DINT phase is a func- tion of the amount of voltage stored on the integrator during the INT phase and the value of VREF. The DINT phase is initiated by the TC520A immediately after the INT phase and terminated when the TC5XX A/D con- verter changes the state of the CMPTR input of the TC520A, indicating a zero crossing. In general, the maximum number of counts chosen for DINT is twice that of INT (with VREF chosen at VININ(MAX)/2). Choos- ing these values guarantees a full count (maximum res- olution) during DINT when VIN =VIN(MAX). The IZ phase is initiated immediately following the DINT phase and is maintained until the CMPTR input transi- tions high. This indicates the integrator is initialized and ready for another conversion cycle. This phase typically takes 2msec. 3.3 Serial Port Control Signals Communication to and from the TC520A is accom- plished over a 3 wire serial port. Data is clocked into DIN on the rising edge of DCLK and clocked out of DOUT on the falling edge of DCLK. READ must be low to read from the serial port and can be taken high at any time, which terminates the read cycle and releases DOUT to a high impedance state. Conversion data is shifted to the processor from DOUT in the following order: OVERRANGE (which can also be used as the 17th data bit), POLARITY, conversion data (MSB first). |
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Ähnliche Beschreibung - TC520 |
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