RCA CDP18S711 manual Memory Read, Tape Write, Tape Read

10 RCA COSMAC VIP Instruction Manual

contained in the last 256-byte page of the on-card RAM. If you have a 2048-byte RAM, you are seeing locations 0700-7FF on the screen. Bit 7 of the byte at 0700 is in the upper left comer. Try storing a sequence of eight AA bytes followed by eight 55 bytes starting at location 0700. Keep repeating this sequence to draw a checkerboard pattern on the screen. There are 32 rows of spots on the screen. Each row represents 8 memory bytes (64 bits). Locations 0700-0707 are shown in the top row, 0708-07OF in the next row down. Draw a bit map on paper and you can construct pictures on the TV screen by entering the proper byte sequences. The byte pattern for displaying the word COSMAC is shown in Appendix A.

Memory Read

Suppose you wish to examine the contents of a memory location. Flip RUN up while pressing key C. Enter the address of the location you want to examine. Press key A for the Memory Read mode. You will see the memory address and the byte stored at that address on the screen. Press any hex key to step through memory and see the contents. Memory locations examined are left unchanged. If a program doesn't run properly you can use this mode to verify that it was stored correctly in memory.

You can now enter and run the short beeper program shown in Appendix A. Flip RUN up with key C pressed. Release key C and enter address 0000. Press key 0 to select the Memory Write mode. Now enter the beeper program one byte at a time using the hex keyboard. Flip RUN down to reset the computer. Flip RUN up to execute the beeper program you just loaded into locations 0000-OOOC. You can load and run any COSMAC VIP program in this manner. For most of the game programs you will first have to load the CHIP-8 interpreter (Appendix C) into locations 0000-OIFF followed by the game program starting at location 0200.

Tape Write

Any program you load into memory will be lost when you turn off power. Unless it is safely stored, you will have to key it in by hand again the next time you want to use it. The cassette interface is provided so that after keying in a program you can then record it on an audio cassette; and when you want to use the program again, all you have to do is play it back into the memory from the cassette. This playback usually takes less than 30 seconds.

The COSMAC VIP cassette interface was designed to work with most standard audio cassette recorders. Panasonic models RQ-309DS, RQ-212D, and RQ-413S have yielded satisfactory results as has the Sony

TC-150. In general, better quality recorders provide more reliable operation.

Your tape recorder must have an 8-ohm earphone or external speaker jack and a microphone input jack. Connect the cassette recorder to the COSMAC VIP tape-in tape-out pads on the right-hand side of the card as shown in the cassette attachment diagram in Appendix A.

After properly connecting your cassette recorder you can try recording and playing back a cassette using the operating system as described below. Follow the cassette recording guidelines provided in Appendix A for best results. If you run into trouble, use the cassette phase and data test procedures described in Appendix A for troubleshooting.

The memory is divided into 256-byte pages for recording. You can record 1 to 15 consecutive pages on tape. The low-order byte of your starting address should be 00. Select the operating system by holding key C down while flipping RUN up. Enter the 4-digit address of the first page to be recorded on tape. Press key F and you're ready to record. Rewind a blank cassette and place your cassette unit in the record mode. Wait about 10 seconds and tap the hex key that represents the number of pages you want to record on tape. The screen will go blank and you'll hear a tone while recording. When the specified number of pages has been recorded on the cassette, the tone will end and the last memory byte recorded on tape will be shown on the screen.

Tape Read

To load memory from a previously recorded cassette, first select the operating system (RUN and key C). Enter the memory address of the first page to be loaded (usually 0000). Press key B to select the Tape Read mode. Rewind and play the cassette. Immediately press the hex key representing the number of pages you want to load into memory from the cassette. The tape recorder tone control should be set to maximum high. The volume control should be set for a steadily glowing tape light when data is being read from the tape. The screen will go blank while the program is loaded from the tape into memory. It will show the last byte loaded into memory at the end of loading.

If the Q light and tone come on while a tape is being read, an error occurred. Flip RUN down, rewind the cassette, and try again. You may h ' ave to readjust the cassette volume control. Be sure that the cassette contains at least as many pages as you specify to be loaded. For most of the game programs, load the CHIP-8 interpreter program (Appendix C) into 0000-