For this week activities, i study deeply about on how to interface the signal in the GSM modem from Programmable Interface Circuit (PIC). So, serial communication interface between micro and pc i must put max232 to convert signal from ttl level (micro) to rs232 level (pc). This is the function of max232 level converter. The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply TIA/EIA-232-F voltage levels from a single 5-V supply. Each receiver converts TIA/EIA-232-F inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V, a typical hysteresis of 0.5 V, and can accept ±30-V inputs. Each driver converts TTL/CMOS input levels into TIA/EIA-232-F levels. The driver, receiver, and voltage-generator functions are available as cells in the Texas Instruments LinASIC library.
MAX232 schematic diagram
The RS232 serial port protocol (v.24) states -15v to represent binary 1 and +15v to represent binary 0. For TTL communication this is incompatible since TTL uses 0v to represent binary 0 and +5v to represent binary 1. MAX232 chip converts serial signal voltage levels to TTL standards, and also vias versa. It therefore has a driver and a receiver to perform this function.
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