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The FM part has '''4 channels''', each having their own operators, panning and amplitude values.
The FM ('''F'''requency '''M'''odulation) is part of the {{Chipname|YM2610}} sound chip. It provides '''4 channels''', each having their own set of 4 operators, panning and amplitude values. It's the most used way of producing music in games.
It's the most used way of producing music in games.


See [[YM2610 registers#FM|YM2610 registers: FM]]
=Common registers=
 
{|class="wikitable"
!Address (Z80 port 4)
!Data (Z80 port 5)
|
|-
|$21
|{{8BitRegister|?|8}}
| Test register. Ignore or set to $00 for normal operation.
|-
|$22
|{{8BitRegister|-|4|On|1|Control|3}}
| LFO control and frequency (see below).
|-
|$28
|{{8BitRegister|Slot (OP4/OP3/OP2/OP1)|4|-|1|Channel|3|}}
| Key On/Off for each channel, with operators control.
|}
 
LFO frequency values are as follows:
*0 – 3.98Hz
*1 – 5.56Hz
*2 – 6.02Hz
*3 – 6.37Hz
*4 – 6.88Hz
*5 – 9.63Hz
*6 – 48.1Hz
*7 – 72.2Hz
 
 
Channel numbering:
{|class="wikitable"
!FM Channel
!Binary Code
|-
  | CH1
  | 001
|-
  | CH2
  | 010
|-
  | CH3
  | 101
|-
  | CH4
  | 110
|}
This strange numbering seems to be due to the fact YM2610 is a YM2610B with 2 removed FM channels (000 and 100).
 
 
 
=Channel registers=
 
Depending on which channel you want to write to, the {{Chipname|Z80}} ports used are different:
* Channels 1 & 2: Ports 4/5
* Channels 3 & 4: Ports 6/7
 
{|class="wikitable"
!colspan=4|Address||colspan=4|Data||rowspan=3|
|-
|CH1||CH2||CH3||CH4||CH1||CH2||CH3||CH4
|-
|colspan=2|Port 4||colspan=2|Port 6||colspan=2|Port 5||colspan=2|Port 7
|-
|$A1||$A2||$A1||$A2
|colspan=4|{{8BitRegister|F-Num 1|8}}
|F-Numbers and Block (1/2)
|-
|$A5||$A6||$A5||$A6
|colspan=4|{{8BitRegister|-|2|Block|3|F-Num 2|3}}
|F-Numbers and Block (2/2)<br/>(must set this first)
|-
|$B1||$B2||$B1||$B2
|colspan=4|{{8BitRegister|-|2|FB|3|ALGO|3}}
|Feedback (FB) and Algorithm (ALGO)
|-
|$B5||$B6||$B5||$B6
|colspan=4|{{8BitRegister|L|1|R|1|AMS|2|-|1|PMS|3}}
|Left (L)/Right (R) output, AM Sense (AMS), and PM Sense (PMS)
|}
 
2CH mode additional operator frequencies:
* OP1 frequency is stored in the usual CH2 frequency registers ($A2/$A6)
* write to Z80 ports 4/5
 
{|class="wikitable"
!colspan=3|Address||colspan=4|Data||rowspan=2|
|-
|OP2||OP3||OP4||colspan="4"|
|-
|$A8||$A9||$AA
|colspan=4|{{8BitRegister|2CH * F-Num 1|8}}
|2CH mode F-Num LSB
|-
|$AC||$AD||$AE
|colspan=4|{{8BitRegister|-|2|2CH * Block|3|2CH * F-Num 2|3}}
|2CH mode F-Num MSB & Block<br/>(must set this first)
|}
 
=Operator registers=
The ranges given for the address represent all of the parameter values. Each channel's operators are laid out as follows:
 
{|class="wikitable"
! Operator || 1 || 3 || 2 || 4
|-
! Channels 1, 3
| $x1 || $x5 || $x9 || $xD
|-
! Channels 2, 4
| $x2 || $x6 || $xA || $xE
|}
 
{|class="wikitable"
!colspan=4|Address||colspan=4|Data||rowspan=3|
|-
|CH1||CH2||CH3||CH4||CH1||CH2||CH3||CH4
|-
|colspan=2|Port 4||colspan=2|Port 6||colspan=2|Port 5||colspan=2|Port 7
|-
|colspan=4|$31-$3E
|colspan=4|{{8BitRegister|-|1|DT|3|MUL|4}}
|Detune (DT) and Multiple (MUL)
|-
|colspan=4|$41-$4E
|colspan=4|{{8BitRegister|-|1|Total Level|7|}}
|Total Level (Volume)
|-
|colspan=4|$51-$5E
|colspan=4|{{8BitRegister|KS|2|-|1|AR|5}}
|Key Scale (KS) and Attack Rate (AR)
|-
|colspan=4|$61-$6E
|colspan=4|{{8BitRegister|AM|1|-|2|DR|5}}
|AM On (AM) and Decay Rate (DR)
|-
|colspan=4|$71-$7E
|colspan=4|{{8BitRegister|-|3|SR|5}}
|Sustain Rate (SR)
|-
|colspan=4|$81-$8E
|colspan=4|{{8BitRegister|SL|4|RR|4}}
|Sustain Level (SL) and Release Rate (RR)
|-
|colspan=4|$91-$9E
|colspan=4|{{8BitRegister|-|4|SSG-EG|4}}
|Envelope generator (not to be confused with the [[SSG]] one)
|}


[[Category:Audio system]]
[[Category:Audio system]]

Latest revision as of 19:32, 18 June 2018

The FM (Frequency Modulation) is part of the YM2610 sound chip. It provides 4 channels, each having their own set of 4 operators, panning and amplitude values. It's the most used way of producing music in games.

Common registers

Address (Z80 port 4) Data (Z80 port 5)
$21
Bit 7 6 5 4 3 2 1 0
Def ?
Test register. Ignore or set to $00 for normal operation.
$22
Bit 7 6 5 4 3 2 1 0
Def - OnControl
LFO control and frequency (see below).
$28
Bit 7 6 5 4 3 2 1 0
Def Slot (OP4/OP3/OP2/OP1) -Channel
Key On/Off for each channel, with operators control.

LFO frequency values are as follows:

  • 0 – 3.98Hz
  • 1 – 5.56Hz
  • 2 – 6.02Hz
  • 3 – 6.37Hz
  • 4 – 6.88Hz
  • 5 – 9.63Hz
  • 6 – 48.1Hz
  • 7 – 72.2Hz


Channel numbering:

FM Channel Binary Code
CH1 001
CH2 010
CH3 101
CH4 110

This strange numbering seems to be due to the fact YM2610 is a YM2610B with 2 removed FM channels (000 and 100).


Channel registers

Depending on which channel you want to write to, the Z80 ports used are different:

  • Channels 1 & 2: Ports 4/5
  • Channels 3 & 4: Ports 6/7
Address Data
CH1 CH2 CH3 CH4 CH1 CH2 CH3 CH4
Port 4 Port 6 Port 5 Port 7
$A1 $A2 $A1 $A2
Bit 7 6 5 4 3 2 1 0
Def F-Num 1
F-Numbers and Block (1/2)
$A5 $A6 $A5 $A6
Bit 7 6 5 4 3 2 1 0
Def - BlockF-Num 2
F-Numbers and Block (2/2)
(must set this first)
$B1 $B2 $B1 $B2
Bit 7 6 5 4 3 2 1 0
Def - FBALGO
Feedback (FB) and Algorithm (ALGO)
$B5 $B6 $B5 $B6
Bit 7 6 5 4 3 2 1 0
Def L RAMS-PMS
Left (L)/Right (R) output, AM Sense (AMS), and PM Sense (PMS)

2CH mode additional operator frequencies:

  • OP1 frequency is stored in the usual CH2 frequency registers ($A2/$A6)
  • write to Z80 ports 4/5
Address Data
OP2 OP3 OP4
$A8 $A9 $AA
Bit 7 6 5 4 3 2 1 0
Def 2CH * F-Num 1
2CH mode F-Num LSB
$AC $AD $AE
Bit 7 6 5 4 3 2 1 0
Def - 2CH * Block2CH * F-Num 2
2CH mode F-Num MSB & Block
(must set this first)

Operator registers

The ranges given for the address represent all of the parameter values. Each channel's operators are laid out as follows:

Operator 1 3 2 4
Channels 1, 3 $x1 $x5 $x9 $xD
Channels 2, 4 $x2 $x6 $xA $xE
Address Data
CH1 CH2 CH3 CH4 CH1 CH2 CH3 CH4
Port 4 Port 6 Port 5 Port 7
$31-$3E
Bit 7 6 5 4 3 2 1 0
Def - DTMUL
Detune (DT) and Multiple (MUL)
$41-$4E
Bit 7 6 5 4 3 2 1 0
Def - Total Level
Total Level (Volume)
$51-$5E
Bit 7 6 5 4 3 2 1 0
Def KS -AR
Key Scale (KS) and Attack Rate (AR)
$61-$6E
Bit 7 6 5 4 3 2 1 0
Def AM -DR
AM On (AM) and Decay Rate (DR)
$71-$7E
Bit 7 6 5 4 3 2 1 0
Def - SR
Sustain Rate (SR)
$81-$8E
Bit 7 6 5 4 3 2 1 0
Def SL RR
Sustain Level (SL) and Release Rate (RR)
$91-$9E
Bit 7 6 5 4 3 2 1 0
Def - SSG-EG
Envelope generator (not to be confused with the SSG one)
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