A COMPUTER SYSTEM ACCOMMODATING PROGRAM CARTRIDGES

Abstract: A microcomputer system employs internal read-only memory devices (3,4) and external read-only memory de­ vices (41,42) in plug-in cartridges (2). Each cartridge includes jumper links (43,44,45,50,51,52) in leads (31,32,33,34,35,36) from the external memories through the cartridge socket (23) to a memory select unit and jumper links (38,39) in leads from earth through the cartridge socket to enable inputs (E) of the internal memories. By linking selected ones of the jumper links in the cartridge, the external memory can be used as an add-on memory or as a base memory replacing the internal memory.

Description: The present invention relates to computer systems which are adapted to employ program cartridges. Program cartridges are at present used in many microcomputer systems. They were first introduced in the field of games computers to provide program data defining different games which can be played. For present purposes, a program cartridge can be regarded as comprising one or more read-only stores mounted on a printed circuit board which includes connection pads for connection to a microcomputer through a socket mounted in the microcomputer. Though, conceivably, the mating connector parts could be reversed, the expected cartridge configuration is typically that shown in U.S. Patent No. 1595156 (Asher and Hardy). The cartridge read-only memory normally contains control code which is additional to control code contained in read-only memory in the microcomputer itself. Thus, in operation, the microcomputer is essentially controlled by the control code held internally and requests extra code for different applications from the cartridge read-only memory. It has now been recognised that in certain conditions, it may be desirable to provide the base control code from a cartridge rather than the internal read-only memories. This enables complete re-configuration of the microcomputer by changing the base control code. It is to effect such change of control that the present invention is directed. WO-A-8 402 206 discloses a computer controlled telephone system in which new features can be forced onto the system by plugging-in program cartridges which have mechanisms thereon which set which system memory, the cartridge memory replaces. There is no cooperative effect between the system and the cartridge setting, the cartridge either disabling or ignoring. IBM Technical Disclosure Bulletin, vol. 22, no. 10, March 1980, pages 4615-4616, disclose a multiple serial cartridge system in which cartridge number (n+1) in the system disables all the previous cartridges in the series. US-A-4 386 773 discloses an extendable cartridge. The present invention provides a configuration which enables the setting of the cartridge to combine with the requirements of the computer system and can be defined as a computer system comprising, in combination, a microcomputer including an internal read-only memory, address means for addressing the memory, select means for selecting the memory, enable means for enabling the memory and a connector (usually a socket) coupled to the address, select and enable means, and one or more program cartridges that can engage the connector, the, or each, cartridge including external read-only memory means coupled to the address means, select means and the enable means through the socket, characterised in that the select means includes a first individually energisable select line coupled to the internal memory and to the connector and second individually energisable select lines or line connected only to the connector, as well as disabling means coupled to the enabling means through the connector via at least one selectively connectable second wiring route in the cartridge, the connection to the select means through the connector being via first and second selectively connectable wiring links between the external memory means and the first and second select lines respectively through the connector, whereby, upon engagement of a cartridge with the connector, the external memory means can selectively supplement or replace the internal memory in accordance with the configuration of the selectively connectable wiring routes and the requirement of the system. In other words, we are considering a smaller data processing system in which cartridges can be configured, by means of links in their wiring, either to provide add-on code to the base code held in internal read-only memory in a microcomputer, leaving the internal code addressable, or to replace the base code by disabling the internal read-only memory and re-directing read-only memory select signals. This is contrasted with the flexible composite memory arrangements normal in larger data processing systems in which code changes can be expected to be achieved by IMPL processes. The present arrangements could be adopted in larger systems, were they to use cartridges, but this seems unlikely at the present time. The present invention will be described further by way of example with reference to one embodiment thereof as illustrated in the accompanying drawing in which the single figure shows a portion of a microcomputer, in particular the read-only memory circuits, and a program cartridge in its pre-plug-in position in relation to the microcomputer The accompanying drawing shows a portion 1 of a microcomputer and a program cartridge 2 which is plug-in into the microcomputer. The microcomputer includes two read-only memory devices 3 and 4. Each of these ROM's includes an address input A, an enable input E, a chip select input S and a data output D. Assuming the ROM's are of 32K size, the address input of each comprises a fifteen line bus 5, coupling an address unit 6 to the ROM address inputs in common. This address unit is coupled to the CPU of the microcomputer to develop these addresses for the ROM's. In addition, the CPU develops three-bit chip select signals, which are decoded by a decoder 7 to provide outputs on lines 8 through 13. In response of a particular three bit pattern, decoder 7 is operable to energise a selected one of lines 8 through 13. In this particular embodiment, six of these lines are provided to select from six ROM's, of which four only are shown. Energisation of one of the lines 8 through 13 selects a ROM through its chip select input S. The enable input E of ROM 3 is coupled to a positive supply line 13 through a resistor 14. Similarly the enable input of ROM 4 is coupled to the supply line through a resistor 16. With cartridge 2 removed from the microcomputer as shown in the figure, the enable inputs E of ROM's 3 and 4 are maintained positive by these couplings so that each ROM is permanently enabled. In operation, an address from address unit 6 together with a select signal on line 9 provides an 8-bit data output on data bus 18 from ROM 3 and an address together with a select signal on line 8 results in a data output from ROM 4. In order to couple cartridge 2 to microcomputer 1, the latter includes a socket 23. This socket includes contacts connected to the chip select lines 8 through 13, the address bus 5, lines 20 and 21 coupled to the resistors in the enable circuits, and the data bus 18. Other contacts (not shown) are coupled to ground and the power supply line to provide ground reference and power to the cartridge. The cartridge includes a plug section 30 containing edge connectors which mate with the socket contacts when the cartridge is inserted into the socket. Reading from left to right, the first six connectors couple lines 31 through 36 on the cartridge to lines 8 through 13 in the microcomputer. The next group of contacts, fifteen in all, couple an address bus 37 to address bus 5 of the microcomputer. Next, two lines couple jumper socket pairs 38 and 39 to enable lines 20 and 21 of the microcomputer. Lastly, the right-most set of connectors couple a data bus 40 to data bus 18 of the microcomputer. When the socket is in position, the two ROM's which it carries have their address inputs coupled in parallel with the address inputs of ROM's 3 and 4 through busses 37 and 5. Similarly, the data outputs of ROM's 41 and 42 are coupled in parallel with the data outputs of ROM's 3 and 4 through data busses 40 and 18. Lines 31, 33 and 35 are connected respectively to one side of jumper socket pairs 43 through 45, the other sides of which are connected in common to the enable input E and chip select input S of ROM 42. Lines 32, 34 and 36 are similarly connected to one side of a further set of jumper socket pairs 50 through 52, the other sides of which are coupled in common to inputs E and S of ROM 41. Ignoring, for the moment, the positions of the jump leads in the figure, we will first look at the operation of the cartridge in the normal mode of operation of cartridges, that is, when it is used as an add-on device providing an extension of the control code contained in the internal ROM's 3 and 4. In such an operation, there are no jump leads in jumper socket pairs 38, 39, 43, or 50. Instead there will be a jump lead in one of jumper socket pairs 44 and 45, and another in one of pairs 51 and 52. As an example, let us say that jumper socket pairs 45 and 52 are bridged. Then, an address on busses 5 and 37 will access ROM 3 when select line 9 from decoder is energised, ROM 4 when select line 8 is energised, ROM 41 when select line 13 is energised and ROM 42 when select line 12 is energised. Note that with the links in jumper pairs 38 and 39 removed, ROM's 3 and 4 are permanently enabled, and that ROM's 41 and 42 are enabled as well as selected by the select lines. Thus, in this particular example, by selection of any one of the select lines 8, 9, 12 and 13, and generation of a ROM address on bus 5, any location of any one of the four ROM's can be accessed. It may be noted here that the six, instead of four select lines are provided to allow another cartridge to be inserted into a further socket in the microcomputer which is connected in parallel with socket 23. Thus, with the six select lines, the system can be expanded by another two ROM's. We will now consider the operation of the system with the jumpers inserted as shown in the drawing. The first thing to note is that the links in jumper pairs 38 and 39 now ground the enable inputs to ROM's 3 and 4, thereby disabling these ROM's. Next, the link in jumper pair 43 directs a chip select signal on line 8 to ROM 42 as well as ROM 4. Similarly chip select line 9 is coupled, through line 32 and the link in jumper pair 50, to ROM 41 as well as its direct path to ROM 3. Thus, when line 8 is now energised, the address on busses 5 and 37 accesses a location in ROM 42 rather than ROM 4. Similarly when chip select line 9 is energised, ROM 41 is accessed rather than ROM 3. Thus, when the jumpers are positioned as shown, the main control of the microcomputer passes from the base ROM's 3 and 4 to ROM's 41 and 42. This means that the microcomputer can be completely reconfigured merely by plugging in the cartridge. If the jumper configuration is altered, it will be obvious how the memory configuration will correspondinglt alter. Typically, a base ROM system may contain power on routines including power on diagnostics, basic input and output routines, operational diagnostics and other operational control routines, such as cassette BASIC routines. Whenever the system is turned on or reset, the processor begins execution under the control of the base ROM system. If, therefore, a cartridge which is configured to re-map the base ROM, the system will begin operation under the control of the cartridge ROM whenever it is turned on or reset. Apart from the re-configuring the system to a particular users exact requirement, the re-mapping of base ROM system to the cartridge ROM system has other advantages. It can, for example, be used by the manufacturer to reset the system directly to a manufacturing test code, defined by the cartridge ROM system, without having to execute the base ROM power on diagnostics. In this operation, error messages could be steered to a communications port, instead of the normally used display system to communicate errors to a central computer test tracking system. Another possible advantage is in the field of copy protection for the cartridge. Since, when the cartridge is plugged into the system, control passes completely to the cartridge code, no system utility can then be used to dump to contents of the cartridge. This, therefore makes it more difficult to copy the cartridge code. It is clear that certain modifications in construction and operation of the system as described can be made. Firstly, the number of ROM's can be varied. For example, the cartridges could each include only one RON, or both the cartridge and the base system could comprise three ROM's. In operation, either one, or both of the base ROM's can be disabled by selection of the links in jumpers 38 and 39. Though the jumpers have been described as jumper sockets, it is clear that their function could be achieved by selectively breaking printed circuit leads on the printed circuit board of the cartridge, or by employing fusable links which could be broken electrically.

Claims: A computer system comprising, in combination, a microcomputer (1) including an internal read-only memory (3,4), address means (6) for addressing the memory, select means (7) for selecting the memory, enable means (13,14,16,20,21) for enabling the memory and a connector (23) coupled to the address, select and enable means, and one or more program cartridges (2) that can engage the connector, the, or each, cartridge including external read-only memory means (41,42) coupled to the address means, select means and the enable means through the socket, characterised in that the select means includes a first individually energisable select line (8,9) coupled to the internal memory and to the connector and second individually energisable select lines or line (10,11,12,13) connected only to the connector, as well as disabling means coupled to the enabling means through the connector via at least one selectively connectable second wiring route (38,39) in the cartridge, the connection to the select means through the connector being via first and second selectively connectable wiring links (43,44;45,50,51,52) between the external memory means and the first and second select lines respectively through the connector, whereby, upon engagement of a cartridge with the connector, the external memory means can selectively supplement or replace the internal memory in accordance with the configuration of the selectively connectable wiring routes and the requirement of the system. A computer system as claimed in claim 1, in which the enabling means comprises a circuit providing, in the absence of a cartridge, a signal level to enable the internal memory, and the disabling means comprises a sub-circuit, which,when connected through the second wiring route and the connector, changes the signal level to disable the internal memory. A computer system as claimed in claim 2, in which the internal memory comprises a plurality of memory units, each having an individual enable circuit coupled thereto, and the disabling means is coupled to each enable circuit through a separate selectively connectable wiring route to the connector. A computer system as claimed in claim 2 or claim 3, in which the enabling means comprise a ground connection in the cartridge. A computer system as claimed in any preceding claim, in which, the internal memory including a plurality of memory units, the select means including a like plurality of individually energisable first select lines (8.9) coupled respectively to the memory units and to the connector, the first selectively connectable wiring links comprising a like number of selectively connectable wiring links between the external memory means and the first select lines through the connector. A computer system as claimed in claim 5, in which the external memory means comprises a plurality of memory units in the, or each cartridge, the select means including a plurality of second individually energisable select lines coupled to the connector, the first selectively connectable wiring links including a plurality of such links coupled to the plurality of second select lines through the connector.

Inventors: KUMMER, DAVID ALLEN, WEBB, GARY EDWARD
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1984
Main classification: G06F12
IPC codes: G11C17, G06F12, G06F13, G06F9, G11C5, G06F17