YMF721

July 10, 1997

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7. Hardware

7-1. ISA bus interface

(1) Data Bus Connect System

Data BUS

Since driving current of data bus, ADB7-0 pins, of YMF721(OPL4-ML2) is about 2 mA (at VDD =

5.0 V), it is recommended to use bus buffer such as LS245 as necessary. At this time, connect ABDIR

pin which outputs bus direction signal of YMF721(OPL4-ML2) with DIR (direction) pin of the bus

buffer such as LS245.

RESET

Reset (RST) pin of YMF721(OPL4-ML2) can be made "H" active or "L" active. When using "H"

active reset, /RESETSEL pin should be open or set to "H", or to "L" when using "L" active reset.

/RESETSEL pin has a built-in pull-up resistor. When this pin is set to "L", the power consumption

increases approximately by 30uA from the one obtained when the pin is open or set to "H".

I/O Channel Ready

In normal operation, the internal data bus of YMF721 (OPL4-ML2) connects the built-in processor

and FM/Wavetable synthesizer blocks. Every time the ISA bus accesses the register for

FM/Wavetable, an internal arbitration circuit causes the internal bus to connect ISA bus and

FM/Wavetable synthesizer blocks. YMF721 (OPL4-ML2) uses I/O channel ready (ARDY pin) as the

internal arbitration circuit. Connect ARDY pin of YMF721 (OPL4-ML2) and IOCHRDY pin of ISA

bus. Although ARDY pin is an open drain output, it is not necessary to attach pull up resistor because

it is usually pulled up at the ISA bus.

(2) No Data Bus Connect System

The input pins ADB7-0, A2-0, /MPUCS, /OPLCS, /IOW and /IOR must be pulled up externally.

Output pins AIRQ, ABDIR and ARDY pins must be open.

7-2. MIDI interface

When using MPU port of YMF721 (OPL4-ML2), RXD and FSP pins must be pulled up. When using

MPU port of the system and receiving MIDI data through RXD pin, FSP pin must be made "L".

7-3. Serial audio interface

YMF721 (OPL4-ML2) outputs clock signals of CLKO (384 fs = 16.9344 MHz), BCO (48 fs =

2.1168 MHz), LRO (fs = 44.1 kHz) and WCO (2 fs = 88.2 kHz) as the serial audio interface. It also

outputs four types of data including DO0 (FM external out), DO1 (Wavetable external out), DO2

(MIX out) and DO3 (effect-send out). Normally, it uses the output of DO2. When YMF721 (OPL4-

ML2) is in power down mode, /PDOUT pin outputs "L" which can be used as the power down control

signal for peripheral systems.