MITS 88-RMB2 User Manual

ROM BASIC Turnkey Module

User’s Manual

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TABLE OF CONTENTS

ABSTRACT................................................................ 1!

SPECIFICATIONS.......................................................... 1!

INSTALLATION............................................................ 2!

THEORY OF OPERATION..................................................... 5!

ASSEMBLY................................................................ 7!

SCHEMATIC DRAWINGS...................................................... 9!

1

88-RMB2

User’s Manual

ABSTRACT

The 88-RMB2 (ROM Basic Turnkey Module) provides MITS Extended Cassette
Basic programming language in Read Only Memory (ROM). Basic is located in
the upper 16K of main memory, addresses 48K through 64K (140000 through
177777 octal). This frees up the lower 48K for the user’s Basic programs.
An automatic startup circuit causes the computer to begin executing Basic
at 140000 (octal) when system power is first applied and after a Reset.

In addition to Basic in ROM, the 88-RMB2 has system functions that allow
the 8800b Turnkey Module to be eliminated.

A serial asynchronous input/output port on the 88-RMB2 interfaces the
system console (or any terminal) to the computer. Most standard baud
rates are available, as well as both RS-232 or TTL signal configurations.
The port can interrupt on input or output. The I/O port addresses are
fixed at 020 and 021 (octal).

The 88-RMB2 provides the signals to the Attaché or 8800bt front panel for
the control switches “STOP/RUN” and “START”, and the system indicators,

1) HLT (HALT), 2) I/O (INPUT/OUTPUT), 3) INTE (Computer interrupts
enabled), 4) INT (Interrupt request) and PWR (+5V Power OK).

The 88-RMB2 also provides sense switch input at port address 377 (octal).

SPECIFICATIONS

Firmware......... Extended Cassette Basic in Read-Only Memory (16K bytes)

(8 2K/* ROM IC’s)

ROM Address: 140000 (octal)

Auto-start....... Fixed address: 140000 (octal)

Activation: Power-on or Reset

Serial I/O Port.. Configuration: RS-232 or TTL
Baud Rate: 110, 300, 1200, 4800, 9600
Fixed I/O Address: 020 and 021 (octal)

Sense Switches... Eight data switches read from I/O port 377 (octal)

Power............ 1 amp at +8V

40 mA at ±18V

Physical......... 5” x 10” printed circuit board

1 slot required

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INSTALLATION

Memory Address

The 88-RMB2 has a hardwired auto-start and non-user addressable ROMs.
The auto-start jumps to the ROM at 140000 (octal). The ROM occupies
memory from 140000 (octal) to 177777 (octal). Make sure your machine
contains no other memory between these addresses.

Sense Switches

I/O port 377 (octal) is reserved for sense switches, at SW-2 on the
88-RMB2 board. These switches may be read by software to control I/O
addressing, stop bits, etc. Unless instructed by a software manual,
these switches will normally be set to produce 000 (octal). Set
switches at SW-2 to the right to produce a 0, and to the left to
produce a 1. Software manuals often uses the words “up” and “down”
when specifying sense switch settings. On the 88-RMB2, “up”
corresponds to left on SW-2, and “down” corresponds to right on SW-2.
Software manuals refer to switch positions A8-A15, which correspond to
SW-2 positions 8-15.

Status Connector

J1 is used to provide machine status to external LEDs located on the
Attaché keyboard or 8800bt front panel. J2 is indexed to prevent
installing the cable incorrectly.

J1 Pin Signal Direction Function

1 +5V Out Power for 8800bt front panel
2 -SHLTA Out Low indicates CPU HALT condition
3 -PINTE Out Low indicates interrupts are enabled
4 -IO Out Low indicates Input or Output cycle
5 -PINT Out Low indicates interrupt requested
6 GND Out Ground reference
7 -POC In CPU reset from front panel STOP switch
8 PRDY In Input from front panel STOP/RUN switch
9 KEY - Pin removed for indexing connector
10 N/C - Not connected

Serial Port

J2 is used for the serial port. J1 is indexed to prevent installing
the cable incorrectly.

J2 Pin Signal Level Direction Function

1 -RTS TTL Out Active-low Request to Send
2 N/C - - Not connected
3 N/C - - Not connected
4 RxD Both In Receive Data
5 -DCD Both In Active low Data Carrier Detect
6 -CTS Both In Active low Clear to Send
7 KEY - - Pin removed for indexing
8 GND - - Ground reference
9 -RTS RS-232 Out Active-low Request to Send
10 TxD Both Out Transmit Data