Jaleco - Moero!! Nettou Yakyuu '88, 256KB ROM, CRC32 68745C64
NEC D7756C 146 sample player with internal 256Kbit ROM, undumped. Same samples as Famicom Moero!! Pro Yakyuu (Black/Red), recording available at http://home.planet.nl/~haps/segali_archive/

4*8KB pages at $4000-$BFFF, initialized to 0.
Mapper chip is exactly the same as ASCII8, except for data bit 7:
a:011ppxxx xxxxxxxx d:sxxbbbbb
a:address, d:data, p: page, b:bank, x:don't care
s:if set, page reads/writes redirect to sample player via a 74HC174, eg. write $80 to $7800 -> $A000-$BFFF = sample player I/O

Sample player (datasheet, 690KB one on http://www.datasheetarchive.com/search.php?t=0&q=uPD7756 ):
reads: always $FF (/BUSY not used)
writes: d:rsxxiiii
i:I0-I3 (sample number, latched on /ST rising edge when not playing)
s:/ST (start), r:1=enable continuous rising edges to /ST (ORed with s), 0=falling edge to /RESET
As I'm unable to measure, s and r bits pin setups are guessed from knowing the behaviour (examples underneath).

examples:
- $C0: nothing
- $80: "strike, strike, strike, strike, ..."
- $80, $C0: "strike"
- $80, short delay, $00/$40: "stri"
- $80, short delay, $81: "strike, ball, ball, ball, ball, ..."

note: writes to sample player are ignored if on page $6000-$7FFF, possibly due to conflict with mapper chip, reads still return $FF though.

eh?

basically what it means is that I need to get a life