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MC145027DW датащи(PDF) 8 Page - Freescale Semiconductor, Inc |
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MC145027DW датащи(HTML) 8 Page - Freescale Semiconductor, Inc |
8 / 20 page MC145026 •MC145027•MC145028•SC41343•SC41344 MOTOROLA 8 OPERATING CHARACTERISTICS MC145026 The encoder serially transmits trinary data as defined by the state of the A1 – A5 and A6/D6 – A9/D9 input pins. These pins may be in either of three states (low, high, or open) allow- ing 19,683 possible codes. The transmit sequence is initiated by a low level on the TE input pin. Upon power–up, the MC145026 can continuously transmit as long as TE remains low (also, the device can transmit two–word sequences by pulsing TE low). However, no MC145026 application should be designed to rely upon the first data word transmitted im- mediately after power–up because this word may be invalid. Between the two data words, no signal is sent for three data periods (see Figure 10). Each transmitted trinary digit is encoded into pulses (see Figure 11). A logic 0 (low) is encoded as two consecutive short pulses, a logic 1 (high) as two consecutive long pulses, and an open (high impedance) as a long pulse followed by a short pulse. The input state is determined by using a weak “output” device to try to force each input high then low. If only a high state results from the two tests, the input is assumed to be hardwired to VDD. If only a low state is obtained, the input is assumed to be hardwired to VSS. If both a high and a low can be forced at an input, an open is assumed and is encoded as such. The “high” and “low” levels are 70% and 30% of the supply voltage as shown in the Electrical Characteristics table. The weak “output” device sinks/sources up to 110 µA at a 5 V supply level, 500 µA at 10 V, and 1 mA at 15 V. The TE input has an internal pull–up device so that a simple switch may be used to force the input low. While TE is high and the second–word transmission has timed out, the encod- er is completely disabled, the oscillator is inhibited, and the current drain is reduced to quiescent current. When TE is brought low, the oscillator is started and the transmit se- quence begins. The inputs are then sequentially selected, and determinations are made as to the input logic states. This information is serially transmitted via the Dout pin. MC145027 This decoder receives the serial data from the encoder and outputs the data, if it is valid. The transmitted data, consisting of two identical words, is examined bit by bit during reception. The first five trinary digits are assumed to be the address. If the received address matches the local address, the next four (data) bits are internally stored, but are not transferred to the output data latch. As the second encoded word is received, the address must again match. If a match occurs, the new data bits are checked against the previously stored data bits. If the two nibbles of data (four bits each) match, the data is transferred to the output data latch by VT and remains until new data replaces it. At the same time, the VT output pin is brought high and remains high until an error is received or un- til no input signal is received for four data periods (see Figure 10). Although the address information may be encoded in tri- nary, the data information must be either a 1 or 0. A trinary (open) data line is decoded as a logic 1. MC145028 This decoder operates in the same manner as the MC145027 except that nine address lines are used and no data output is available. The VT output is used to indicate that a valid address has been received. For transmission security, two identical transmitted words must be consecutively re- ceived before a VT output signal is issued. The MC145028 allows 19,683 addresses when trinary lev- els are used. 512 addresses are possible when binary levels are used. PIN DESCRIPTIONS MC145026 ENCODER A1 – A5, A6/D6 – A9/D9 Address, Address/Data Inputs (Pins 1 – 7, 9, and 10) These address/data inputs are encoded and the data is sent serially from the encoder via the Dout pin. RS, CTC, RTC (Pins 11, 12, and 13) These pins are part of the oscillator section of the encoder (see Figure 9). If an external signal source is used instead of the internal oscillator, it should be connected to the RS input and the RTC and CTC pins should be left open. TE Transmit Enable (Pin 14) This active–low transmit enable input initiates transmission when forced low. An internal pull–up device keeps this input normally high. The pull–up current is specified in the Electri- cal Characteristics table. Dout Data Out (Pin 15) This is the output of the encoder that serially presents the encoded data word. VSS Negative Power Supply (Pin 8) The most–negative supply potential. This pin is usually ground. VDD Positive Power Supply (Pin 16) The most–positive power supply pin. MC145027 AND MC145028 DECODERS A1 – A5, A1 – A9 Address Inputs (Pins 1 – 5) — MC145027, Address Inputs (Pins 1 – 5, 15, 14, 13, 12) — MC145028 These are the local address inputs. The states of these pins must match the appropriate encoder inputs for the VT pin to go high. The local address may be encoded with trinary or binary data. D6 – D9 Data Outputs (Pins 15, 14, 13, 12) — MC145027 Only These outputs present the binary information that is on encoder inputs A6/D6 through A9/D9. Only binary data is acknowledged; a trinary open at the MC145026 encoder is decoded as a high level (logic 1). Din Data In (Pin 9) This pin is the serial data input to the decoder. The input voltage must be at CMOS logic levels. The signal source driv- ing this pin must be dc coupled. |
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