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John Haugabook d57d5dfcdf Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

2026-01-18 23:59:45 -05:00

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AS6C62256 32K x 8 Low-Power CMOS SRAM Specification

1. Overview

The AS6C62256 is a 256 Kbit (32K x 8) low-power CMOS static random-access memory (SRAM) manufactured by Alliance Memory (and second-sourced by others). It is fully compatible with common 28-pin SRAM pinouts and is widely used in 6502, Z80, and other 8-bit microprocessor systems for read/write memory.

The device offers fast access times, simple control logic, and very low standby power consumption.

2. General Characteristics

Feature	Description
Memory size	256 Kbits (32 KB)
Organization	32,768 x 8 bits
Data bus	8-bit
Address bus	15-bit (A0-A14)
Technology	CMOS SRAM
Access time	55 ns / 70 ns (variant dependent)
Operating voltage	5 V ± 10%
Standby current	< 1 µA (typical)
Package types	DIP-28, SOJ-28, TSOP-28

3. Pin Configuration (Logical)

3.1 Address Pins (A0-A14)

Select one of 32,768 memory locations
Address must be stable during read or write cycle

3.2 Data Pins (I/O0-I/O7)

Bidirectional tri-state data bus
High-impedance when not enabled

3.3 Control Pins

Pin	Description
CE#	Chip Enable (active low)
OE#	Output Enable (active low)
WE#	Write Enable (active low)
VCC	+5 V power supply
GND	Ground

4. Memory Organization

Linear address space from $0000 to $7FFF
Each address corresponds to one byte (8 bits)

Address range: 0000h - 7FFFh
Data width:    8 bits

5. Read Operation

5.1 Read Cycle Conditions

Signal	State
CE?	LOW
OE?	LOW
WE?	HIGH

Data becomes valid after access time (tAA)
Outputs remain valid while CE? and OE? are LOW
Outputs are high-impedance when CE? or OE? is HIGH

6. Write Operation

6.1 Write Cycle Conditions

Signal	State
CE?	LOW
OE?	HIGH or LOW
WE?	LOW pulse

Data is written on the rising edge of WE? or CE?
Address and data must be stable during write window
No internal write delay (true SRAM behavior)

7. Timing Notes (Summary)

Parameter	Typical
Address access (tAA)	55-70 ns
CE? access (tACE)	55-70 ns
OE? access (tOE)	25-35 ns
Write cycle time	≥ 55 ns

8. Power Modes

8.1 Active Mode

CE? = LOW
Normal read/write operation

8.2 Standby Mode

CE? = HIGH
Data retained
Very low power consumption

9. Reset and Power-Up Behavior

No reset pin required
Data is undefined at power-up
Memory contents preserved only while VCC is present

10. Typical System Integration (6502 Example)

Mapped at:     $0000 - $7FFF
CE?   decoded address
OE?   R/W?
WE?   inverted R/W?

11. Absolute Maximum Ratings (Summary)

Parameter	Rating
VCC	-0.5 V to +6.5 V
Input voltage	-0.5 V to VCC + 0.5 V
Storage temp	-65 °C to +150 °C

12. Compatible and Equivalent Devices

Device	Notes
AS6C62256	Alliance Memory
CY62256	Cypress
HM62256	Hitachi
KM62256	Samsung
IS62C256	ISSI

13. Common Use Cases

Main RAM for 6502 / Z80 systems
Video buffers and frame memory
Embedded systems requiring fast R/W memory
Retrocomputer SBC designs

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