Aster CT-80 port usage

255, FFh (TRS-80 Model 1 compatible cassette and MODESEL control)

bit 0-1  W: cassette data output bit 0. Only the patterns 00, 01 and 10 are used.
bit 2  W: cassette motor relay. 0 = off, 1 = on
bit 3  W: video MODESEL control 0 = 64/80 characters, 1 = 32/40 characters.
bit 6 R : video MODESEL state.
bit 7 R : cassette data input bit. Writing to port FFh resets the data input flip-flop.

Note switching between two cassette recorders is done via memory location 37E4h, bit 0

254, FEh (MEMORY MAP port)

bit 0  W: CPU clock; 0 = 1.77 MHz, 1 = 3.54 MHz
bit 1  W: BOOT ROM active; 0 = BOOT ROM not at 0000h-07FFh, 1 = BOOT ROM at 0000h-07FFh
bit 2  W: BASIC active; 0 = BASIC active, 1 = BASIC inactive (RAM at 0000h-2FFFh)
bit 3  W: MEMORYMAP; 0 = TRS-80 mode, 1 = CP/M mode
bit 4  W: HALT operation; 0 = HALT* generates NMI*, 1 = HALT* stops CPU
bit 5  W: Memory Mapped devices; 0 = Memory Mapped devices active, 1 = only RAM in memory
bit 6  W: -
bit 7  W: -

253, FDh (6845 VDU register data port)
bit 0-7 RW: note some registers are read-only, others write-only, it varies with the VDU type.

252, FCh (6845 VDU register address port plus video mode and deglitcher control)
bit 1-3  W: 6845 register address
bit 4  W: enable TRS80 mode
bit 5  W: enable CP/M mode
bit 6  W: enable deglitcher
bit 7  W: disable deglitcher

232 - 235, 0E8h - 0EBh UART


Aster CT-80 memory mapped devices

Keyboard
3800h - 3880h. Mirrors up to 3BFFh
3801h R    ; Keyboard row 0: @, A, B, C, D, E, F, G
3802h R    ; Keyboard row 1: H, I, J, K, L, M, N, O 
3804h R    ; Keyboard row 2: P, Q, R, S, T, U, V, W
3808h R    ; Keyboard row 3: X, Y, Z, [, \, ], ^, _
3810h R    ; Keyboard row 4: 0, 1, 2, 3, 4, 5, 6, 7 
3820h R    ; Keyboard row 5: 8, 9, :, ;, ,, -, ., /
3840h R    ; Keyboard row 6: Enter, Clear, Break, (arrows), Space
3880h R    ; Keyboard row 7: SHIFT, ESC, F0, F1, Ctrl, F3, F4

3800h - 3880h  W: The interrupt vector for the Aster keyboard interrupt mechanism.


37E0h-37E3h  W  Motor on (pulsed by mono-stable flip-flop), 
                bit 0-3: Drive select, 
                bit 4: side select, 
                bit 5: clock speed select
37E0h-37E3h R   Reset Real Time Clock interrupt,
                bit 6: FDC interrupt,
                bit 7: RTC interrupt (40Hz)
37E4h-37E7h  W  Cassette drive latch
37E8h-37EBh R   Printer control bits
             W  Printer data latch and strobe
37ECh R   Status Register
37ECh  W  Command Register  (writing FEh selects single density, writing FFh selects double density)
37EDh RW  Track Register
37EEh RW  Sector Register   (writing C0h selects 8" disk drive, writing A0h selects 5 1/4" disk drive)
37EFh RW  Data Register