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Memory Map and Data Entry Mode

Memory Map

The table below outlines how the full 64Kb of address space is allocated on the TEC-1G.

Address	Contents	Type
0000H-00FFH	Reserved for Z80 instructions	RAM
0100H-07FFH	PATA/SD Drive area or free RAM	RAM
0800H-087FH	Reserved for hardware stack	RAM
0880H-0FFFH	Reserved for monitor RAM	RAM
1000H-3FFFH	Free RAM	RAM
4000H-7FFFH	Free RAM (protected)	RAM
8000H-BFFFH	Expansion socket	RAM/ROM
C000H-FFFFH	Monitor ROM	ROM

Some things to be considered are:

• Any RAM location can be updated, but it is highly recommended not to update Monitor Reserved RAM locations. This can/will cause undesirable effects on the running of the TEC. A Cold Reset will restore the TEC to its default running state (hopefully).
• The address range between 4000H-7FFFH is a special area that can be made READ ONLY. This is called a Protected area. Protect mode can be switched on using the configuration 3-DIP switch. If protect is enabled and code is being executed. No RAM update can be done in this range. This feature is designed to protect keyed-in code from being inadvertently erased by a rogue routine.
• The Expansion Socket on the TEC can have a 32Kb ROM or RAM inserted. Only 16Kb can be accessed at one time. To switch between high and low memory use the Expand switch on the configuration 3-DIP switch. The switch can also be overridden in software by toggling the Expand flag in the Settings menu or pressing Fn-E.
• If the monitor ROM is a legacy monitor, IE: Mon1, Mon2, JMon or BMon, The address range 0000H-07FFH will be READ ONLY and will emulate the same addressing that is used for that particular ROM. Shadow mode will be active by default and will be indicated by an illuminated LED segment on the system latch BAR component.

Data Entry Mode

Data Entry Mode allows the user to enter Z80 Op Codes directly into the TEC. To access Data Entry Mode from the Main Menu, simply press the AD key. In this mode, the 4 left seven-segment displays will show the current editing address, and the 2 right segments will display the byte at that address.

The decimal place LED on the segments indicates which part, Address or Data, is currently enabled for direct updates. In the picture above, the dots are on the Data segments.

The initial starting address is 4000H. This address was chosen as it’s within the Protect RAM area.

Basic Operation

To update a byte at an address, simply use the 0-F keys on the keypad. After the byte has been entered, by default when the next byte is keyed, the current editing address will automatically move to the next address location. This saves the user from pressing the Plus key after each byte is added. This option can be switched off in the Settings menu.

To navigate to another address, press the Plus or Minus key. Or press the AD key. When using the AD key, the decimal place dots will move to the address segments, indicating that the address field is updatable. Key a new 16-bit address using the 0-F keys. Press the AD key to move back to data updating mode.

And finally, to execute code, navigate to the address where the code starts and press the GO key. Protect mode will be honoured if switched on. If the code ends with a RET instruction (C9), execution will cleanly exit back to the monitor. The LCD screen will display the code start address while running.

One thing to note is that while data is being entered, the decimal place LED on the data segments will change from displaying two lights to one. The one light will indicate which Nibble (half byte) has been entered. This will help know if the whole byte has been entered or not.

If a mistake is made during data entry and the byte is to be re-entered. To stop the address from automatically incrementing, press the AD key twice. This will reset the Nibble counter and allow a new byte to be entered.

If any key is held down, after a short period, the key will automatically repeat. This is mostly useful while holding down the Plus or Minus key to quickly move to a new address. But can also be used to populate memory with 00 or FF or anything else.

LCD Screen

In Data Entry Mode, the LCD Screen will display 12 bytes of data. 4 bytes before the current editing location and 8 bytes from the current editing location. These bytes are displayed in groups of 4 (3 lines). A right arrow indicates the byte at the current editing location.

Displayed on the right side of the screen is the current edit mode, da=Data, ad=Address, the current byte in LCD ASCII and the Nibble Counter. The picture below shows: The current address is 4000, Data mode, “>” = 3E in ASCII and 0 nibble count.

On the 4th line of the LCD, the Z80 Assembly of the current OP Code(s) is shown. This can be useful to see what instruction is currently being keyed.

By displaying a range of bytes on the LCD, the user can check if the correct bytes have been entered without individually moving to each address.

Function Keys

Various extra options can be selected via the Function Key. To use these functions, hold the Fn key down and press any other key.

The routines attached to the Function Key are:

Shortcut	Routine	Description
Fn-AD	Main Menu	Display the Main Menu.
Fn-0	Save Current Address	Press 1, 2 or 3 to save the current editing address in RAM so you can quickly jump to this location later. Three addresses can be saved. This is useful if your code is in a location other than 4000H and the Reset button has been pressed. Press AD to exit the routine. The initial default address is 4000H.

Shortcut	Routine	Description
Fn-1, Fn-2, Fn-3	Quick jump to Address	Move the monitor’s current editing location to the saved address set by Fn-0.
Fn-4	Intel Hex Load	Shortcut to the Main Menu routine.
Fn-5	Toggle GLCD Term	Use the GLCD as a terminal.
Fn-6	Save Session	Save all RAM to disk. Requires the PATA Drive or Micro SD Card Expansion boards. See Hard Drive Access for more information.
Fn-7	Restore Session	Load session from disk. Requires the PATA Drive or Micro SD Card Expansion boards. See Hard Drive Access for more information.
Fn-8	Fill with NOPs	Fill a selected area of memory with NOP instruction 00H. Provide a from and to address and confirm by pressing C.
Fn-A	Restore from Backup	Reverse of the Fn-B routine. Defaults the To/From/Dest addresses to copy back from backup. Values can still be modified if necessary.
Fn-B	Block Backup	Shortcut to the Main Menu routine.
Fn-C	Smart Block Copy	Shortcut to the Main Menu routine.
Fn-D	Disassembly View	Switch between Data Entry View and Disassembly View. Disassembly View displays the next 4 assembly instructions. To move through the instructions, press the Plus or Minus keys. Data entry can still be done in this mode if desired.

Shortcut	Routine	Description
Fn-E	Toggle Expand	Toggle the Expansion Socket Expand flag. This switches between the upper and lower memory of the 32Kb ROM/RAM in the expansion socket.
Fn-F	Catalog	Catalog the Drive and list files for loading. Requires the PATA Drive or Micro SD Card Expansion boards.
Fn-Plus	Insert Byte	Insert an NOP instruction at the current editing location and move all bytes up to max RAM by one address upwards. It will also do a Smart Block Copy to all moved bytes. This routine can add a Breakpoint (F7) or missing opcodes to an existing program.
Fn-Minus	Delete Byte	Delete a byte from the current editing location and move all bytes down by one address. It will also do a Smart Block Copy to all moved bytes.
Fn-Reset	Cold Reset	Perform a Cold Reset. This resets the TEC to its default state.

Matrix Keyboard

Keyboard Connection

Mon3 will work with the TEC QWERTY or Mechanical Matrix Keyboard Add-on. The Keyboard is connected to the Keyboard Socket on the lower left of the PCB. How your Keyboard PCB is designed might affect which pins can be connected. Please view the TEC-1G Schematic for information on pin configuration.

To activate the Keyboard, The Matrix switch on the 3-DIP switch is to be turned on. This activates the Matrix Keyboard and disables the onboard Hex Keypad (except Reset). Mon3 only maps keys present on the TEC-1G to the Matrix Keyboard.

The Keyboard map to Hex Keypad is as follows:

Hex Keypad	Matrix Keyboard	Hex Keypad	Matrix Keyboard
AD	Esc	GO	Enter
Plus	Right Arrow	Minus	Left Arrow
0-F, Fn	0-F, Fn keys	Reset	Reset key, if connected

The full range of keys can be accessed and converted when developing programs via the matrixScan and matrixToASCII API routines.

Debugging Programs

Breakpoints

Breakpoints can be inserted within a program which can help with viewing the state of the CPU registers. To break the execution of your code, insert RST 30H or F7 at the current address where the break should occur.

An easy way to insert a byte into an existing program is to press Fn-Plus. This will insert a NOP instruction at the current address. Then change this byte to F7.

When the execution of code is interrupted with a breakpoint, the TEC will pause and display register information on the LCD screen.

Register Display

The contents of the Z80 CPU registers AF, HL, BC, DE, IX, IY, the Program Counter and Stack Pointer are displayed. CPU Flags are also displayed. Flags that are set are in Capitals. To continue code execution press the GO key and to quit execution and return to the Monitor press the AD key. Finally, to remove an inserted Breakpoint press Fn-Minus at the address where the Breakpoint is. This will remove the breakpoint and adjust the code to its original state.

Warning: Breakpoints will be ignored if a connection is made between the + and D5 pins on the G.IMP header. Do not connect the + pin to the - pin on the G.IMP header. This will short out the TEC.

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