Oki OKIFAX 5750 Service Manual page 834

Service Guide OKIFAX 5750/5950 Page:
Chapter A Board Descriptions
A3.1.6 CPU Peripheral Circuits
Memory
(1) DRAM
Size: 8 Mbytes (4 megabits x 16 bits; One chip)
Drive voltage: 3.3 V
The basic control signal is generated by the bus state controller incorporated in the CPU.
(2) Flash ROM
Size: 1.5 Mbytes (512K bits x 16 bits + 256K bits x 16 bits; A total of two chips)
Peripheral elements
(1) Clock
A real-time clock IC (serial I/F) incorporating a crystal oscillator is used. Its basic frequency is 500 Hz. CPU pins 110 (RTCTXD), 109 (RTCDATA), and 112
(RTCCLK) are used as I/F signal pins. The drive voltage is 3 V and backed up by a dedicated lithium battery.
(2) Speaker drive circuit
A tone switching output board is used to switch between the 2441 Hz waveforms output from the LSI chip (IOGA5), issuing various buzzer sounds, key touch
sound, ringing tone and line monitor sounds.
A block diagram is shown below.