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Casio PB-2000C - hardware

The microprocessor

On this page only information specific to the PB-2000C is shown. See the PB-1000 hardware page for more general information about the microprocessor and the bus waveforms.

Decoded address ranges for the chip select signals

CS0: &H10000..&H17FFF, built-in RAM 32kB
CS1: &H18000..&H1FFFF, built-in RAM extension 32kB and the default address range for the RP-33 module (when pad 4 is open and pad 5 soldered)
CS2: &H28000..&H2FFFF, alternative address range for the RP-33 module (when pad 5 is open and pad 4 soldered)
CS3: &H30000..&H3FFFF, unused
CS4: &H00D90..&H0FFFF, unused
CS5: &H04000..&H05FFF, expansion port
CS6: &H00C10..&H00C11, gate array (memory configuration registers)
CS7: &H00C00..&H00C0F, gate array (excluded locations), serial, printer and FDD interface

Function of individual bits of the 8-bit port

P7..P6 drive the piezo-buzzer
P5 is the reset output for peripherals
P4 controls the FDD power, 0 turns the power on
P3 selects the FDD transfer direction, 1 when writing to the FDD interface, 0 when reading from the FDD interface
P2 is the FDD transfer direction acknowledge input
P1 senses the card presence (low voltage level when a card is inserted)
P0 selects the language version, connected through a jumper either to VSS (English PB-2000C) or to GND (Japanese AI-1000)

The gate array

gate array pin functions

Pin functions

PinSymbol Function
1ROM0 chip select output for the internal ROM with the C interpreter, active low, decodes address range &H00000..&H0FFFF with exclusion of segments decoded by outputs ROM2 and ROM3
2ROM1 not used, decodes fixed address range &H10000..&H2FFFF
3ROM2 selects the card slot pin 20, decoded address range specified with the register &H00C10
4ROM3 selects the card slot pin 33, decoded address range specified with the register &H00C11
5power sense receives high level from the S8054ALR battery monitor chip when valid supply voltage is present
6power switch receives low voltage level when the power switch is turned on and the card locked
7VSS negative supply voltage
8SW this output drives the microprocessor pin 36, low voltage level turns the system on
9inverted VDD senses the microprocessor pin 33 state through an inverter built with a pnp transistor
10CS7 low level at this input disables the ROM0..ROM3 signals, used to exclude the address range &H00C00..&H00C0F occupied by the FA-7/FD-100 interface
11CS6 chip enable input for the configuration registers, receives low level from the CPU for the address range &H00C10..&H00C11, low level at this input disables the ROM0..ROM3 signals
12..19IO0..IO7 bi-directional data bus
20WR bus write strobe signal, active low
21GND positive supply voltage
22RD bus read strobe signal, active low
23OE data strobe control signal
24VEXT control low voltage level enables the LCD driver power supply
25..28A0, A15..A17 address bus

Configuration registers - function of individual bits

register bit enabled combination of address bits decoded address range
A17..A15 = 000
A17..A15 = 001
A17..A15 = 010
A17..A15 = 011
A17..A15 = 100
A17..A15 = 101
A17..A15 = 110
A17..A15 = 111

The actual decoded address range of the first memory segment is limited to &H00C12..&H07FFF. Apart from the excluded memory locations &H00C00..&H00C11, the CPU never puts an address below &H00C00 to the external bus.

Bits 2 and 3 of the configuration register must not be set due to bus conflicts with the RAM in the memory bank 1.

Example configurations

Configuration word = &H0000
This configuration is used by the built-in C interpreter. The chip select signals ROM2 and ROM3 are disabled. The built-in ROM is enabled in the memory bank 0.
Configuration word = &H0003
This configuration is used by the BASIC language card OM-53B. The chip select output ROM2 maps the BASIC card to the memory bank 0. The built-in C interpreter ROM is disabled.
Configuration word = &H0010
This configuration is used by the system for scanning the memory cards. The chip select output ROM2 maps the card to the memory bank 2, which allows accessing data below the location &H0C12.
Configuration word = &H0043
This configuration is used by the DL-Pascal compiler card. The lower half of the Pascal ROM is additionally mapped to the memory bank 3 for data access below the location &H0C12.

The ROM card socket

  01 - VSS        16 - IO5        31 - A17
  02 - A12        17 - IO6        32 - GND
  03 - A7         18 - IO7        33 - ROM3
  04 - A6         19 - GND        34 - GND
  05 - A5         20 - ROM2       35 - GND
  06 - A4         21 - A10        36 - NC
  07 - A3         22 - RD         37 - NC
  08 - A2         23 - A11        38 - NC
  09 - A1         24 - A9         39 - NC
  10 - A0         25 - A8         40 - NC
  11 - IO0        26 - A13        41 - NC
  12 - IO1        27 - WR         42 - NC
  13 - IO2        28 - A14        43 - NC
  14 - IO3        29 - A15        44 - P1
  15 - IO4        30 - A16        45 - GND

pin 20 - ROM2 chip enable (gate array pin 3)
pin 33 - ROM3 chip enable (gate array pin 4)
pin 44 - microprocessor port P1, senses the card presence, connected to VSS inside the card

The flexible strip connecting the CPU board with the LCD board

flexible strip signals

VEXT is the LCD driver supply voltage of ca. -7V

The keyboard

The columns of the keyboard matrix are driven from the 12-bit KO output port, controlled by the IA register. A pressed key makes contact between selected column and row. The rows are sensed by the 12-bit KI input port, accessible through the KY register.

keyboard layout

Mapping of the KY register bits to the keyboard rows:

KY register bit mapping

The RAM expansion module connector

RAM expansion module connector

The peripheral port connector

peripheral port connector