The orginal text is found at: www.geocities.com/SiliconValley/Peaks/6869/cpu.html some pins has been added by Johan Borg johbo050@student.liu.se -- >Thanks to Bryan Christopher Turner Pin # / What it does 1 / R6 2 / R7 used for battery level detection in the TI89 3 / R8 -"- 4 / R8 -"- 5 / LCD FS normaly a pulse every 11ms (90Hz) 6 / LCD BS normaly ~740 kHz 7 / LCD ? 50/50 45Hz 8 / LCD RS norm pulse every 88uS (11.5kHz) 9..12 / LCD data 13 / Gnd 14 / Vcc 15 / reset? 16 / CS4/ (memory at $C0 0000, note that this signal was found because of what appears a bug 17 / CE1/ (ROM at $40 0000) ; in some keypressed-detecting code, which generates a 18 / CE odd byte ; write to somewhere in this area for some keys, 19 / CE even byte ; might be bad if you use this signal for access to extra ram) 20 / R/W 21 / CE2 (RAM chip select) 22 / D11 23 / D3 24 / D10 25 / D2 26 / D9 27 / D1 28 / D8 29 / D0 30 / CE3/ (ROM at $20 000) 31..38 / A1..A8 39..40 / A18..A19 41 / Vcc 42 / Gnd 43 / D4 44 / D12 45 / D5 46 / D13 47 / D6 48 / D14 49 / D7 50 / D15 51..59 / A17..A9 60 / ? (seams to output exactly the same thing as pin 51/A17 61 / A20 62 / link out (tip) (to base of transistor in Q1) 63 / link out (ring) (to base of transistor in Q1) 64 / link in (tip) (connected to pullup resistor, connected to port via D10 and L2) 65 / link in (ring) (connected to pullup resistor, connected to port via D10 and L3) 66 / Vcc 67 / Gnd 68 / OSC2/2 used for voltage multiplier generating ~16v for the LCD 69 / pin 68 inverted used for voltage multiplier generating ~16v for the LCD 70..73 / LCD constrast LSB-MSB 74 / low=LCD on 75..80 / R0-R5 81 82 / ON key 83 / C0 84 / 85 / Gnd(?) 86 / Vcc(?) 87 / OSC 2 in 88 / C1 89 / OSC 2 out 90..91 / C2..C3 92 / OSC 1 out 93 / C4 94 / OSC 1 in 95 96..98 / C5..C7 99 / used as the input for battery level detection. (can be set to output by using 600000:6,4 100 / output-pin, controlled by $600000:7,5 used for LSB in contrast on TI-92, unused on TI-89 Rx = keyboard ROW address line Cx = keyboard COLUMN line