SLAS070 - D2819, NOVEMBER 1983 - REVISED SEPTEMBER 1986
The TLC532A and TLC533A are monolithic LinCMOSTM peripheral integrated circuits each designed to interface a microprocessor for analog data acquisition. These devices are complete peripheral data acquisition systems on a single chip and can convert analog signals to digital data from up to 11 external analog terminals. Each device operates from a single 5-V supply and contains a 12-channel analog multiplexer, and 8-bit ratiometric analog-to-digital (A/D) converter, a sample-and-hold circuit, three 16-bit registers, and microprocessor-compatible control circuitry. Additional features include a built-in self-test, sixmultipurpose (analog or digital) inputs, five external analog inputs, and an 8-pin input/output (I/O) data port. The three on-chip data registers store the control data, the conversion results, and the input digital data that can be accessed via the microprocessor data bus in two bytes
(most-significant byte first). In this manner, a microprocessor can access up to 11 external analog inputs or 6 digital signals and the positive reference voltage that may be used for self-test. The A/D conversion uses the successive-approximation technique and switched-capacitor circuitry. This method eliminates the possibility of missing codes, nonmonotonicity, and a need for zero or full-scale adjustment. Any one of 11 analog inputs (or self-test) can be converted to an 8-bit digital word and stored within 10 us for the TLC532A or 20 us for theTLC533A after instructions from the microprocessor are recognized. The on-chip sample-and-hold circuit automatically minimizes errors due to noise on the analog inputs. Furthermore, differential high-impedance reference inputs are available to help isolate the analog circuitry from the logic and supply noises while easing ratiometric conversion and scaling.
The TLC532AI and TLC533AI are characterized for operation from - 40°C to 85°C. The TLC532AM and TLC533AM are available in both the N and FN plastic packages and are characterized for operation from - 55°C to 125°C.
The TLC532A and TLC533A provide direct interface to a microprocessor-based system. Control of the TLC532A and TLC533A is handled via the 8-line TTL-compatible 3-state data bus, the three control inputs (R/W\, RS, and CS\), and the CLK input. Each device contains three 16-bit internal registers -- the control register, the analog conversion data register, and the digital data register.
A high level at the R/W\ input and a low level at the CS\ input set the device to output data on the 8-line data bus for the processor to read. A low level at the R/W\ input and a low level at the CS\ input set the device to receive instructions into the internal control register on the 8-line data bus from the processor. When the device is in the read mode and the RS input is low, the processor reads the data contained in the analog conversion data register. However, when the RS input is high, the processor reads the data contained in the digital-data register.
The control register is a write-only register into which the microprocessor writes command instructions for the device to start A/D conversion and to select the analog channel to be converted. The analog conversion data register is a read-only register that contains the current converter status and most recent conversion results. The digital data register is also a read-only register that holds the digital input logic levels from the six dual-purpose inputs.
Internally each device contains a byte pointer that selects the appropriate byte during two cycles of the CLK input in a normal 16-bit microprocessor instruction. The internal pointer automatically points to the most significant (MS) byte after the first complete clock cycle any time that the CS\ is at the high level for at least one clock cycle. The device treats the next signal on the 8-line data bus as the MS byte. A low level at the CS\ input activates the inputs and outputs and an internal function decoder. However, no data is transferred until the CLK goes high. The internal byte pointer first points to the MS byte of the selected register during the first clock cycle. After the first clock cycle in which the MS byte is accessed, the internal pointer switches to the LS byte and remains there for as long as CS\ is low. The MS byte of any register may be accessed by either an 8-bit or a 16-bit microprocessor instruction; however, the LS byte may only be accessed by a 16-bit microprocessor instruction.
Normally, a 2-byte word is written or read from the controlling processor, but a single byte can be read by the processor by manipulating the CS\ input. This can be used to read conversion status from the analog conversion data register or the digital multipurpose input levels from the digital data register. The format and content of each 2-byte word is shown in Figures 1 through 3.
A conversion cycle starts after a 2-byte instruction is written to the control register and the start conversion (SC) bit is a logic high. This 2-byte instruction also selects the input analog channel to be converted. The status (EOC) bit in the analog conversion data register is reset, and it remains reset until the conversion is complete, at which time the status bit is set again. After conversion, the results are loaded into the analog conversion data register. These results remain in the analog conversion data register until the next conversion cycle is complete. If a new conversion command is entered into the control register while the conversion cycle is in progress, the on-going conversion is aborted and a new channel acquisition cycle begins immediately.
The reset input R\ allows the device to be externally forced to a known state. When a low level is applied to the R\ input for a minimum of three clock periods, the SC bit is cleared. The A/D converter is then idled and all the outputs are placed in the high-impedance off-state. However, the content of the analog conversion data register is not affected by the R\ input going to a low level.
Detailed information on interfacing to most popular microprocessors is readily available from the factory.
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