TRS-IO gives a TRS-80 Model 1/III online capabilities and provides access to a variety of services. TRS-IO currently features the following capabilities:

1. Access to the RetroStore
2. FreHD emulation
3. Access to files mounted on a SMB share or located on a micro-SD card
4. Access to remote servers via TCP
5. Virtual printer support

The TRS-IO versions for the Model 1 have some additional features that are explained below. The following sections give an overview of TRS-IO as well as setup instructions. This Github repository contains the complete source code as well as the KiCad schematics for the PCB (Printed Circuit Board). For the following descriptions it is assumed that an assembled TRS-IO card is available.

The figure below depicts the overall architecture. The TRS-80 machine is connected to TRS-IO via the I/O Bus. TRS-IO has a WiFi module that connects to the local WiFi router. This allows TRS-IO to connect to the Internet and access various services. Note that TRS-IO can only connect to a 2.4 GHz WiFi network.

TRS-IO requires a TRS-80 Model III with 48kB of RAM or a Model 1 with 16kB of RAM. Floppy disk drives or a cassette tape are not required.

TRS-IO support TRS-IO comes in three different versions:

• TRS-IO for the Model III
• TRS-IO for the Model I using a builtin 32kB SRAM
• TRS-IO for the Model I using an FPGA

In the following, each of the versions is explained in detail.

The following figure shows the top view of the TRS-IO card for the Model III:

1. Power supply via a micro-USB connector
2. Multi-color status LED
3. Status button
4. TRS-80 I/O bus connector
5. Micro-SD card reader
6. Disable FreHD jumper

The TRS-IO card needs to be connected to the TRS-80 Model III's I/O Bus via a 50-pin ribbon cable (4). Furthermore, the TRS-IO card needs a separate power supply via a standard 5V USB charger. The micro-USB connector (1) plugs into the side of the TRS-IO card. The push button (3) and the multi-color status LED (2) will be explained in the configuration section.

The following figure shows the top view of the TRS-IO card for the Model 1:

1. Power supply via a micro-USB connector
2. Multi-color status LED
3. Status button
4. TRS-80 I/O bus connector
5. Micro-SD card reader

The TRS-IO version for the Model 1 is almost identical to the Model III. One difference is the I/O bus connector (4) is compatible with the 40-pin expansion interface of the Model 1. There are several additional features for the Model 1 version that are not relevant to the Model III version:

• A 32kB SRAM chip for a total of 48kB of total RAM.
• 25ms heartbeat timer to trigger the realtime clock.
• FreHD auto-boot for an unmodified M1.

The TRS-IO project features a second version for the Model 1 that makes use of an FGPA (Field Programmable Gate Array). Using an FPGA allows for some advanced features not possible with the SRAM edition of TRS-IO. The following figure shows the top view of the FPGA version for the Model 1:

1. Power supply via a micro-USB connector
2. Multi-color status LED
3. Status button
4. TRS-80 I/O bus connector
5. Micro-SD card reader
6. N/A
7. VGA connector
8. A15/VU configuration jumpers

This version of TRS-IO offers all the features of the SRAM edition of TRS-IO as outlined in the previous section. Additionally, the FPGA edition also offers a VGA connector (7) that can be used instead of a CRT monitor. This version of TRS-IO also emlates the LE18 graphics cards. The color of the VGA signal can be set to white (X=0), green (X=1), and amber (X=2) via the following OUT statements:

OUT 31,0:OUT 31,5:OUT 31,X

There are two configuation jumpers (8): With the VU jumper, the ESP also powers the FPGA. When using this jumper, the FPGA SHOULD NOT be powered via its own micro-USB connector; power should only be supplied to the ESP's micro-USB connector (1). The A15 jumper regulates the address range the FPGA responds to. Without the A15 jumper, the FPGA only responds to memory read/write requests for the upper 32 kB (essentially mimicking the upper RAM of the SRAM edition). With the A15 jumper, the FPGA will respond to the complete 64kB address space of the Z80. This requires a modified Model 1 as the FPGA also responds to ROM read requests.

The core of the TRS-IO card is an ESP32 microcontroller that features a WiFi module that is used to connect to a WiFi router. After physically connecting the TRS-IO card to a TRS-80 Model 1/III as explained in the previous sections, the WiFi module on the ESP32 microcontroller first needs to be be configured with the credentials of the local WiFi network.

While in setup mode, the TRS-IO's status LED will continuously blink in white to indicate that it has not yet been configured. While in that mode, TRS-IO will create an open access point called "TRS-IO". Use a laptop to connect to this WiFi network and then use a browser to visit URL trs-io.local. The following web page should appear in the browser:

Some hosts do not correctly handle mDNS that is used to resolve trs-io.local. In that case, visit the IP address 192.168.4.1 instead. The web interface shown above can be used to configure SSID and password of the WiFi network that TRS-IO should connect to, the local timezone as well as the credentials of a SMB share. For open networks leave the WiFi password field empty. Note that TRS-IO cannot connect to WiFi networks that use a capture portal. The timezone as well as the SMB share are not required but will result in limited functionality.

Once all the information is provided, click on submit to upload the parameters. TRS-IO will automatically reboot and try to connect to the specified WiFi network. If successful, the LED will turn green for a few seconds. If the credentials are wrong or if the specified WiFi network is not accessible, the LED light will turn permanently red.

Note that TRS-IO will store all parameters in its local flash memory, so the setup only needs to be performed once. Once TRS-IO is connected to a WiFi router, it should still be possible to access URL trs-io.local from a browser on the same WiFi network. If mDNS is not supported by the host, the following BASIC program can be used to determine TRS-IO's local IP address that was assigned by the router:

10 OUT 236,16
20 OUT31,0:OUT31,4
30 C=INP(31):IF C=0 THEN END
40 PRINT CHR$(C);
50 GOTO 30

The web interface will also display two icons to indicate the status of the SMB share and the micro-SD card (see screenshot above). Green icons indicate that TRS-IO has access. Red icons indicate an error. In that case, hovering the mouse over the red icon will display the error message. It should be noted that TRS-IO needs to be rebooted whenever a micro-SD card is inserted or ejected.

Pushing the status button will make the LED flash twice. The first time for the WiFi status (green: WiFi connected; red: WiFi not connected) and a second time for the SMB status (green: connected to SMB share; red: not connected to SMB share). With proper configuration parameters, the LED should flash green twice. Holding down the push button for more than three seconds will erase all configuration parameters and place TRS-IO back into setup mode (status LED flashing white). This might be necessary if TRS-IO is moved to a different WiFi network.

The status LED indicates the state of TRS-IO:

• Blinking white: TRS-IO is not configured. It will create an open WiFi access point named "TRS-IO"
• Solid green: when TRS-IO has been configured with WiFi credentials and TRS-IO was able to connect to the WiFi network, the status LED will light in solid green for several seconds.
• Solid red: TRS-IO was configured with WiFi credentials but it was not possible to connect to the specified network. The reason could be wrong credentials or the specified network is itself offline. The push button can be used to reset TRS-IO into setup mode in case different credentials need to be provided.
• Solid blue: TRS-IO performs an OTA (Over-the-Air) update. TRS-IO will automatically detect newer firmware versions and will download and install the new firmware. The status LED will light solid blue during this process.
• Off: the status LED will be off during regular operations when TRS-IO is connected to the specified WiFi network and ready to accept commands from the TRS-80 Model III.

TRS-IO is compatible with the popular FreHD hard disk emulator. The FreHD disk images can either be stored on a SMB share or on a micro-SD card. If a micro-SD card is inserted, it will take precedence over a mounted SMB share. Once TRS-IO is configured to access a SMB share, simply copy the required files such as FREHD.ROM to the SMB share. Alternatively, the disk images can be transferred to the micro-SD card. The IMPORT/EXPORT utilities will access files on the SMB share or micro-SD card respectively.

TRS-IO support a virtual printer interface. Visiting trs-io.local/printer from a browser will open the printer interface. Any printer output from the M1/MIII will be displayed in the printer interface. If the host cannot resolve the mDNS name trs-io.local, the above BASIC program can be used to determine the TRS-80's IP address.

The RetroStore hosts applications for the Tandy Radio Shack vintage computers and allows to seamlessly download and run these applications without the need of cassettes or floppy disks. TRS-IO acts as a gateway to the RetroStore. This requires to run a program on the TRS-80 that interfaces with TRS-IO. This program is available as a regular CMD executable. For TRS-80 machines with attached physical floppy disks, this CMD executable can be copied to a floppy disk and launched the usual way. For TRS-80 machines that have neither floppy disk drives nor cassette drives, it is also possible to bootstrap the native client via the following short BASIC program:

10 OUT236,16
20 OUT31,3
30 OUT31,1
40 N=INP(31)+256*INP(31)
50 FOR X=1 TO N:POKE20735+X,INP(31):NEXT
RUN
SYSTEM
*? /20736

The above BASIC program will download the CMD executable from TRS-IO and launch the native client. Note that this procedure needs to be repeated every time the TRS-80 is turned on.

After successfully launching the native RetroStore client, the monitor of the TRS-80 should look like this:

The screenshot above shows the main menu of the native RetroStore client. The arrow indicates the currently selected menu item. The up and down cursor keys can be used to move between the various menu items. Hitting the ENTER key will activate the currently selected menu item. Pressing CLEAR or BREAK in sub-menus will return to the previous menu.

Keyboard controls:

• Cursor up/down: toggle menu selection
• ENTER: select current menu selection
• BREAK/CLEAR: exit to previous screen