DESCRIPTION
The SM3508 is a CMOS 4-bit single-chip microcomputer for databank incorporating data memory RAM, LCD driver (the output is adjustable in 16 steps for various contrast), key/switch input circuit, 8-bit parallel I/O port, 2 output ports and buzzer output circuit. The chip also has memory expansion controlling feature. One of two ports contains special output circuit for infrared (IR) communication. By connecting an external crystal, a 1 Hz timer is made possible for easier clock function.

FEATURES
• ROM capacity :
   Program ROM 12 k x 23 bits
   Character ROM 6 x 8 x 256 bits
   Constant ROM 1 k x 4 bits
• RAM capacity :
   Working RAM 256 x 4 bits
   Display RAM 74 x 16 bits
   Data RAM 3 k x 8 bits
• Memory expansion (external) : 1M x 8 bits x 3
• LCD display : 74-segment x 16-common
• I/O ports :
   Parallel I/O 8 bits
   Input 2 bits
   Output 2 bits
   Buzzer output 1 bit (4 kHz)
   Key input 6 bits
• Standby release : 2 events (2 Hz signal, key input)
• Built-in oscillator :
• Instruction cycle time : 3 µs
• Operating temperature : –10 to + 60°C
• Supply voltage : 2.5 to 5.5 V
• Package : 128-pin QFP (QFP128-P-2828)
   [Test Sample only]
   System clock (built-in CR oscillator) 1 MHz
   (external ceramic resonator) 1 MHz
   Timer (built-in CR oscillator) 32.8 kHz
   (external crystal) 32.768 kHz