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MAX7348AEP+ Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX7348AEP+ Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 29 page 2-Wire Interfaced Low-EMI Key Switch and Sounder Controllers 6 _______________________________________________________________________________________ too many interrupts. The key-switch status can be checked at any time by reading the key-switch FIFO. A 1-byte read access returns both the first key-press event in the FIFO (if there is one) and the FIFO status, so it is easy to operate the MAX7347/MAX7348/ MAX7349 by polling. If the INT pin is not required, it can be configured as an open-drain general-purpose output (GPO) capable of driving an LED. The MAX7349 monitors up to 64 keys. The MAX7348 monitors up to 40 keys. The MAX7347 monitors up to 24 keys (Table 1). If the application requires fewer keys to be scanned, up to six of the key-switch outputs can be configured as open-drain GPOs capable of driving LEDs. For each key-switch output used as a GPO, the number of key switches that can be scanned is reduced by eight. An alert logic input (MAX7349 only) can be configured to deliver an automatic, customizable sound and/or an interrupt on every falling edge of the logic input. The logic state of the alert input can be read at any time. Tone Generator The piezo sounder controller generates a square wave with the frequency of a musical tone under processor con- trol. The selection of tones covers the 5th musical octave (523.25Hz to 987.77Hz), plus seven other notes up to 2637Hz. The sounder output is also programmable to be either high or low for the entire sound duration to operate an electronic sounder, relay, or lamp instead of a piezo transducer. The sound duration is programmable from 15.625ms in seven binary steps up to a maximum of 1s. The piezo sounder controller interface uses a single 1- byte access to its own separate slave address. Commands are double-buffered to allow two commands (2 bytes) to be stored and executed in succession. The sounder controller performs the transition between queued sound commands without click artifacts. The controller can also autoloop between the two most recent commands. Autolooping allows a wide range of intermittent and two-tone sounds to be initiated, and then run automatically without further intervention. Key-Scan Controller Key inputs are scanned statically, not dynamically, to ensure low-EMI operation. As inputs only toggle in response to switch changes, the key matrix can be routed closer to sensitive circuit nodes. The key controller debounces and maintains a FIFO of key-press events (including autorepeated key presses, if autorepeat is enabled). Figure 1 shows keys order. Serial Interface Figure 2 shows the 2-wire serial interface timing details. Serial Addressing The MAX7347/MAX7348/MAX7349 operate as slaves that send and receive data through an I2C-compatible 2-wire interface. The interface uses a serial data line (SDA) and a serial clock line (SCL) to achieve bidirec- tional communication between master(s) and slave(s). A master (typically a microcontroller) initiates all data transfers to and from the MAX7347/MAX7348/MAX7349 and generates the SCL clock that synchronizes the data transfer. The MAX7347/MAX7348/MAX7349s’ SDA line operates as both an input and an open-drain output. A pullup resistor, typically 4.7k Ω, is required on SDA. The MAX7347/MAX7348/MAX7349s’ SCL line operates only as an input. A pullup resistor, typically 4.7k Ω, is required on SCL if there are multiple masters on the 2-wire inter- face, or if the master in a single-master system has an open-drain SCL output. Each transmission consists of a START condition (Figure 3) sent by a master, followed by the MAX7347/ MAX7348/MAX7349 7-bit slave address plus R/W bit, a register address byte, 1 or more data bytes, and finally a STOP condition. Start and Stop Conditions Both SCL and SDA remain high when the interface is not busy. A master signals the beginning of a transmis- sion with a START (S) condition by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it issues a PART PACKAGE- PINS MAXIMUM KEY SWITCHES INT OUTPUT KEY- SCAN SLAVE IDs SOUNDER SLAVE IDs SOUNDER OUTPUT GPOs ALERT INPUT MAX7349 24 64 Yes 4 4 Yes 6 + 1 ( INT) Yes MAX7348 20 40 Yes 4 4 Yes 3 + 1 ( INT)— MAX7347 16 24 Yes 1 fixed — — 1 + 1 ( INT)— Table 1. Product Features Table |
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