NESdev Wiki, “APU Pulse”

Cite as: NESdev Wiki, “APU Pulse”
Original: https://www.nesdev.org/wiki/APU_Pulse
sha256: 8d06b0f473613f45c2db1cb4c3054085d520407c924ca2908311267906c5ce55
Version: oldid 23444
Archived: https://web.archive.org/web/20260629094247/https://www.nesdev.org/wiki/APU_Pulse
Accessed: 2026-10-21
Licence: none stated on the page
Credit: NESdev Wiki editors (nesdev.org); see the page history.
Notes: Read from the Wayback capture of 2026-06-29 (revision 23444). Used for the duty-cycle sequences and the pulse frequency formula.

Cited on

The APU has two pulse channels, each with four duty settings, 12.5%, 25%, 50%, and 25% negated (75%), as 8-step sequences.	`leadSequencer behavior`	Wiki
A pulse channel's frequency is $f = f_{C P U} / (16 (t + 1))$ for an 11-bit timer period $t$ , with $f_{C P U}$ = 1.789773 MHz on NTSC; periods below 8 silence the channel.	`Pulse channel output to mixerPulse channel output to mixer`	Wiki
A note byte is an offset into `FreqRegLookupTbl`, a table of 51 two-byte timer periods that the driver writes to the channel's timer registers; a recreation turns period $t$ into $f_{C P U} / (16 (t + 1))$ Hz on a square channel and half that on the triangle.	`Pulse channel output to mixer`	Code