M381: 768 Byte ROM + 18 Byte RAM

The M381 is a ROM and RAM including:

• 765 words of 8 bits of Read Only Memory.
• 18 words of 8 bits of Random Access Memory,
• The 11 bit registers Q, RA, RB, Z. These are organized as a Stack and the information stored in them can be moved up and down by control commands.
  In some cases the Z register is used to address the ROM:
  the selection of Q or Z is done by the control logic and is a function of the control lines status. The Q and Z register contents can be changed by storing ADB bits 3/2/1 into Q bits 11/10/9 or Z (bits 11/10/9) and DAB into Q or Z (bit 8 to 1): this is done by commands decoded from the control lines.
• Two I/0 ports of 8 bits:s
  Through each I/0 port it is possible to transfer information into the data bus from 8 lines of a peripheral or to store the data bus information into 8 flip-flops whose output is connected to the same 8 lines.
• The masked module code assigned to the unit during system design and the logic to compare this code with the informations on the address bus.

More details: M380 uP System and Instruction Set. SGS/ATES