9845 Mouse Project
Why and How
At the design time of the HP 9845, human interaction already was an important issue for computer systems, however a computer mouse was not part of the concept. Instead, several other pointer devices were offered, like digitizers, light pens or graphic tablets. Even the arrow keys could be used to position a cursor, and some plotters could be used in a reverse mode to feed their position back into the host system. But no mouse was available. Not for the HP 9845 and not for any other system, except the famous Xerox Alto, which had been the grandfather prototype platform for many of the modern human engineering concepts, including a window based graphical user interface or - using a computer mouse as pointing device.
Ok, the HP 9845 didn't have a mouse support. But there were enough other means for positioning and pointing. So, where is the problem?
- The HP 9111A graphics tablet is rare, the light pen is very rare, and the digitizer is super rare. If you like to use the interactive graphics features of the 9845, you'll in most cases have to be satisfied with the arrow keys.
- Theoretically, it could be possible to connect a standard serial mouse via a serial interface to the 9845. And just as it is with climbing high mountains, if it can be done, this is reason enough to do it.
So I tried and I was surprised how good it works.
A Brief History of Computer Mice
As far as we know today, the computer mouse as a pointing device goes back to the years 1963/1964, when Douglas C. Engelbart and his collegue William English worked with their team at the Stanford Research Institute (SRI) on different pointing devices for computer systems. First presentation to the public was at the autumn summit of the American Federation of Information Processing Societies (AFIPS). Later in 1970 Engelbart received patent US3541541 for an "X-Y Position Indicator for a Display System". Doug Egbart's construction was based on two wheels, which were mounted in a 90° angle. William English changed over to the Xerox Palo Alto Research Center (PARC), where the ball mouse was developed with its first use in the Xerox Alto in 1973.
Doug Engelbarts' Original Mouse Prototype
First commercial applications were with the Xerox Star in 1981 and the Apple Lisa in 1983, however both with limited commercial success. This changed completely with the Apple Macintosh in 1984, where the concepts previously prooved with the Lisa were implemented in a convenient, coherent and - most important - affordable manner.
I personally was immediately convinced when playing around in 1984 with an early Macintosh, that this concept would conquer the mainstream market. The 80's proceeded with the ball mouse as standard, low-cost pointing device for most subsequent systems. The IBM PC, when launched in 1981, actually didn't yet support mice pointers (in fact, the graphical user interface was completely missing). The PS/2 series was the first officially offering a mouse device for the PC, the PS/2 mouse, in 1987. In the end of the 90's, the optical mouse started to displace the ball mouse, offering a more accurate and less dirt sensitive tracking mechanism.
Original Macintosh Mouse and Modern Optical Mouse
The first mice did have ony one button, as did the original prototype of Doug Engelbart and the first Lisa and Macintosh mice. The first Microsoft and PS/2 mice already provided two buttons, and Logitech presented the first sucessfully selled three-button mouse in 1985 (perfect example of making business by just adding a simple but useful feature). Commercial workstations generally used three-button mice, especially when operated with X Window based GUIs.
Operating a Serial Mouse with an HP9845
Prerequisites
For using the mouse as a pointer device with an HP9845, you need
- a 98036A RS-232C serial interface (either standard with DTE connector or option 001 with DCE connector),
- an RS-232C serial microsoft compatible mouse,
- if required, an 9-to-25-pin adaptor for connecting the mouse to the 98036A serial interface, plus
- one of the Assembly Language option ROMs (either the Assembly Execution or the Assembly Execution & Development ROM).
A 98046A datacomm interface should also work, however since I do not own one, I've never tested.
98036A opt. 001 Serial Interface, Standard 9-pin-to-25-pin
Adaptor and Logitech 3-button Mouse
Because a serial mouse device operates as a DCE (data communication equipment), the normal connection of a serial mouse device is via a 98036A opt. 001 interface. If the mouse has a 9-pin SUB-D connector, you can use a standard 9-pin-to-25-pin adaptor with the following wiring:
| 9-pin Mouse (female) |
25-pin 98036A opt. 001 (male) |
Signal |
| 1 | 8 | DCD (Data Carrier Detect) |
| 2 | 3 | RxD (Receive Data) |
| 3 | 2 | TxD (Transmit Data) |
| 4 | 20 | DTR (Data Terminal Ready) |
| 5 | 7 | GND (Signal Ground) |
| 6 | 6 | DSR (Data Set Ready) |
| 7 | 4 | RTS (Request to Send) |
| 8 | 5 | CTS (Clear to Send) |
| n/c | n/c | RI (Ring Indicator) |
| Shield | Shield | Shield |
If using a 98036A standard serial interface (which usually connects to DTEs), the 9-to-25-pin adaptor must have a null-modem wiring:
| 9-pin Mouse (female) |
25-pin 98036A Standard (female) | Signal | |
| DCD (Data Carrier Detect) | 1 | 8 | DCD (Data Carrier Detect) |
| RxD (Receive Data) | 2 | 2 | TxD (Transmit Data) |
| TxD (Transmit Data) | 3 | 3 | RxD (Receive Data) |
| DTR (Data Terminal Ready) | 4 | 6 | DSR (Data Set Ready) |
| GND (Signal Ground) | 5 | 7 | GND (Signal Ground) |
| DSR (Data Set Ready) | 6 | 20 | DTR (Data Terminal Ready) |
| RTS (Request to Send) | 7 | 5 | CTS (Clear to Send) |
| CTS (Clear to Send) | 8 | 4 | RTS (Request to Send) |
| RI (Ring Indicator) | n/c | n/c | RI (Ring Indicator) |
| Shield | Shield | Shield | Shield |
Preparations
The 98036A interface has to be configured to a data rate of 1,200 baud, there is a second small switch at the side of the interface (NOT the select code switch on the upper side of the interface!) which has to be set manually to 5 (=1,200 baud). The select code actually doesn't matter as long as no other interface uses the same select code, however it is recommended to use select code 10 for the 98036A standard interface and select code 11 for the 98036A opt. 001 interface.
The Microsoft Serial Mouse Protocol
I've chosen the Microsoft serial mouse for a test since most serial mice do support the communication protocol used by this standard type of computer mouse. Note that the PS/2 mouse works slightly different and is neither compatible to RS-232C nor to the serial mouse protocol.
The original Microsoft mouse has two buttons and two axis. In contrast to e.g. a graphics tablet, not the absolute position is transmitted to the host, but the relative movement. For communication, an RS-232C connection is used with 1,200 baud, no parity, 7 data bits and one stop bit (1200-N-7-1). The power supply is done via the RTS and DTR lines, so both lines must be permanently set positive by the host for proper operation.
Data is sent to the host with each mouse event, which in turn is triggered either by pressing or releasing a button or by mouse movement. Each event generates a package of three bytes, with the following meaning:
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
+----+----+----+----+----+----+----+----+
Byte 1: | X | 1 | LB | RB | Y7 | Y6 | X7 | X6 |
+----+----+----+----+----+----+----+----+
Byte 2: | X | 0 | Y5 | Y4 | Y3 | Y2 | Y1 | Y0 |
+----+----+----+----+----+----+----+----+
Byte 3: | X | 0 | X5 | X4 | X3 | X2 | X1 | X0 |
+----+----+----+----+----+----+----+----+
With bit 7 of each byte as 'don't care'-bit, bit 6 as sync bit for indicating a new byte sequence, LB as the left button state with LB=0 if released and LB=1 if pressed, RB as the right button state, Y7..Y0 as signed vertical motion and X7..X0 as signed horizontal motion (both in 2's complement notation if negative). Both motion values are in the range of -128 to +127.
The Mouse Driver Implementation
A good mouse driver should
- capture all mouse data,
- work in the background without disturbing the running user program,
- control the hardware cursor directly without the user program involved,
- activate appropriate handler routines in the user program as required,
- be capable to be enabled and disabled as needed,
- support both text and graphics mode.
The normal use would be in a BASIC program, however for proper operation the mouse driver itself must be programmed in assembly language, and therefore requires an Assembly Execeution or Assembly Execution and Development option ROM installed. Actually, the mouse driver is a perfect example for how the interrupt I/O system of the HP9845 can be used.
First, there has to be a routine which registers another routine, the interrupt service routine (ISR), as system level handler for all interrupts generated from serial input. The routine also has to do further initializations, like setting up the proper communication parameters for the serial line and enabling the interface. Once registered, each byte of serial input data generates a call to the interrupt service routine, which then takes the byte from the interface, performs the appropriate operations on this byte, and finally tells the interface to accept the next byte from the mouse device.
When all three bytes are complete, the interrupt service routine checks whether one of the conditions are met which had been previously requested from the BASIC user program (like button up or button down events), issues the events to the running BASIC program, and updates the cursor position.
Finally, two other routines are required: one for setting mouse parameters like the type of events the BASIC program is interested in or the type of graphical cursor which should be displayed, and another routine for terminating (de-installing) the mouse driver.
For the notification from the interface to the interrupt service routine, system-level interrupts are used. For the communication from the ISR to the BASIC program, BASIC level interrupts are used. Both have a certain relation in that every BASIC level interrupt is the result of a change in the input data, which again is triggered by a system-level interrupt. However, the BASIC program defines which type of change it wants to be notified for.
I wrote a sample driver (simply called "Mousedriver") which demonstrates how to implement and use interrupt-driven system-level I/O and which uses the following assembly language routines to perform the tasks decribed above:
Mouse_on(<select_code>)
Installs the driver for the serial interface with select code <select_code>, which is usually either 10 or 11 for serial interfaces.
Mouse_set(<event_mask>, <cursor_type>)
Configures which events should be reported to the user program, and which cursor type should be displayed on mouse movement. <event_mask> is a combination of 1 for right button up, 2 for right button down, 4 for left button up and 8 for left button down events, all logically or'ed together. <cursor_type> is either 0 for no cursor, or 1 for a full screen cursor, or 2 for a small cross blinking cursor, or 3 for an underline blinking cursor. All hardware cursors require graphics mode.
Mouse_get(<event>, <lbutton>, <rbutton>, <xpos>, <ypos>)
Retrieves the current mouse state, including the latest events delivered from the system-level interrupt service routine to the BASIC user program (as logically or'ed combination of the events mentioned above), the current state of the mouse buttons and the current absolute position of the pointer (independent whether the cursor is visible or not). <lbutton> and <rbutton> are returned as 0 for button down and 1 for button up. <xpos> is in the range between 0 and 559, <ypos> in the range of 0 to 454. Origin is the upper left screen corner.
Note that the button up/down event(s) which originally caused the notification and which are documented in <event> are not necessarily identical with the current state of the mouse buttons.
Mouse_off
Initiates a shut-down of the mouse driver*.
All routines are used inside a BASIC program with a preceeding ICALL statement. The implementation is quite generic and should work in any 9845 system, however it has been tested on a 9845B with graphics option.
Generally, there are two types of use. Once the mouse driver is installed, the mouse state can either be interrogated in regular intervals (polling) by calling the Mouse_get() routine, or a mouse events can be directed to a special BASIC routine (which then calls the Mouse_get() routine). For most cases, the latter option is the better solution, since mouse events can be immediately handled.
An appropriate BASIC event handler can easily be implemented with
INTEGER Event,Lbutton,RButton,Xpos,Ypos
ILOAD "MSDRVA" ! Load mouse driver assembly module
Sc=10 ! Select code for serial interface
ICALL Mouse_on(Sc) ! Install mouse driver
ON INT#Sc GOSUB Mouse_handler ! Define mouse notification handler
ICALL Mouse_set(8+2,2) ! Enable notifications on left & right button down
...
Event_loop: GOTO Event_loop
...
Mouse_handler: ! Notification handler for mouse events
ICALL Mouse_get(Event,Lbutton,Rbutton,Xpos,Ypos)
... do something with the data ...
RETURN
where Sc is the select code of the serial interface. In order not to disturb the user program, some critical operations (especially DMA transfers) must not be interrupted, so there has to be a way to disable the generation of mouse initiated interrupts. The general procedure for quickly disabling and re-enabling interrupts generated from serial input data is via the statements
WAIT WRITE Sc,5;0 (for disabling serial interrupts)
... do some critical procedures in between ...
WAIT WRITE Sc,5;132 (for re-enabling serial interrupts)
where Sc is again the select code of the serial interface. These commands should always be used for disabling interrupts during graphics draw operations (which normally are using DMA transfers).
As a conclusion, the mouse driver works fine with the 9845 architecture, and it's too bad a mouse wasn't available at the design time of the system.
*Note that mouse driver shutdown actually has to be performed from within the system-level interrupt service routine (ISR), so it can require to make a short mouse move or click after calling the Mouse_off routine in order to definitly terminate the driver. Otherwise, an Error 193 can be the result of an IDELETE statement because there is still an active handler which can't be deleted.
A Sample Mouser Driver Graphics Demo Application
As an example how to use the mouse driver, some keyboard events and, in addition, how to utilize the graphics features of a 9845B, I've written a small drawing program which uses both mouse and keyboard control, quite similar to common painting programs.
The demo provides a canvas which can be freely drawn or filled with lines, rectangular frames or solid rectangles. Arbitrary text labels can be input with the keyboard. Line and fill type and color can be selected as well as the cursor type. Objects can be either drawn or erased. The whole artwork can be sent to the internal printer or saved/loaded to/from mass storage at any time (of course in an uncompressed format...). Note that color primarily refers to the 9845C, however <k8> is used to activate the (single) color on monochrome displays whereas SHIFT+<k8> selects the erase mode.
Mouse Graphics Demo Help Screen
Due to the limited graphics perfomance of the 9845B in BASIC there is no eraser, however the whole screen can be cleared. Finally, there is a special help screen with a summary of the used function keys which can be activated with the <HOME> key.
The save and load feature for graphics supports both fast saves (BDAT files) and standard saves (DATA files). As fast saves consumes only half the disc space and works five times as fast as the standard save, this is the recommended way. However, fast saves are only possible on disc media, so if you want to save to tapes, you'll have to use the standard save. Once saved and transferred to PC, both file types can be converted to standard Windows BMP bitmap files with the Bmpconvert program from the 9845 Utilities Project. Also, a standard BMP file can be converted to a BDAT or DATA file, transferred to the 9845 and then loaded with the MSDEMO program. See the Tutorial on Using Bitmaps for more information.
Hardware accelerated vectors, polygons or circles, as well as "rubber bands" are supported with enhanced or color graphics only and are not used in the demo program. Storing canvas data currently is supported only for monochrome graphics.
Have fun and send me some of your favorite creations. Here is a first try (note the mouse cursor at the upper right..):
Something is different...
Downloads
Click here for downloading an hpi image file with MS mouse driver and mouse graphics demo, as well as the program listings:
| Image with mouse driver and demo application: | 9845-mouse-driver-hpi.zip |
| Mouse driver and demo application listings: | 9845-mouse-driver-listings.zip |