TRS-80 Model III

Model I compatible all-in-one with internal switching supply, monitor and up to two drives.

Also: Model III (26-1061, 26-1063)
Year: 1980
CPU: Z80 @ 2.02752 MHz (10.1376 MHz / 5)
RAM: 4, 16 or 48 KB (4116 DRAM)
ROM: 14 KB Model III BASIC (8 + 4 + 2 KB ROMs)
Video: 64 × 16 or 32 × 16 text, 128 × 48 graphics; 1 KB of 2114 video RAM; built-in 12-inch monitor
Sound: None built in
OS: Model III BASIC (Level II compatible); TRSDOS 1.3 with disks

Chips

Chip	Where	Role
Z80A CPU	U77	Main CPU (8-bit, 40-DIP)
4116 DRAM 16K x 1	U7-U14 ($4000-$7FFF), U25-U32 ($8000-$BFFF), U43-U50 ($C000-$FFFF)	Dynamic RAM, 16K x 1 (lower 16K on the Spectrum)
2114 SRAM 1K x 4	U81, U82 (video RAM)	Static RAM (ZX80 and ZX81 1K)
2364 Mask ROM 8K×8	U104 (ROM A, MCM68A364)	BASIC and KERNAL ROMs (C64); BASIC and KERNAL (VIC-20, PET); character ROM (C128)
2332 Mask ROM 4K×8	U105 (ROM B)	Character ROM (C64, VIC-20, PET)
9316B / 2316B ROM 2K x 8	U106 (ROM C) and U36 (character generator MCM68A316E)	2K x 8 mask ROM: Apple II monitor and BASIC ROMs; TRS-80 ROM C and character generator
WD FD1793 floppy disk formatter/controller	U7 on the FDC board (Sams)	Single and double density disk controller on the Model III and Model 4 FDC boards, ports F0H-F3H.

I/O bus (J2, underside), 50-pin PCB edge (25 + 25) UNVERIFIED
Printer port (card edge), 34-pin PCB edge (17 + 17) UNVERIFIED
Cassette (rear DIN, from header J3), 5-pin DIN socket (180°) UNVERIFIED
RS-232C (P1 on the optional RS-232 board), DB-25 UNVERIFIED
Main supply outputs (SK2, SK3, SK4), Locking 4-pin PCB headers on the power supply board
Monitor board input (J101) from CPU board J5, 10-position edge on the RCA video monitor board (position 5 keyed)

Rail	Expect	Measure at
+5 V	4.75-5.25 V; ripple under 50 mV p-p into the resistive test load only	Z80A pin 11; m3-psu pin 4 (SK2)
+12 V	11.40-12.60 V; ripple under 150 mV p-p into the resistive test load only	4116 pin 8; m3-psu pin 2 (SK2)
-12 V	-11.0 to -15.0 V	m3-psu pin 1 (SK2)
-5 V	About -5 V	4116 pin 1; MC7905C output