Fluke 2625A, 2635A service manual 2A-74.PCMCIA Memory Card Connector

Theory of Operation (2635A) 2A

Detailed Circuit Description

The Memory Card Controller provides a register based interface for the Microprocessor to use to access data stored on industry standard PCMCIA memory cards. A 26 bit counter controls the address bus (CA<0> through CA<25>) to the PCMCIA Memory Card Connector (A6P1). An eight bit data bus(CD<0> through CD<7>) and memory card control signals (REG*, CE1*, CRD*, and CWR*) control accesses to memory on the card.

The REG* signal (A6U1-8) is like an additional address bit. When REG* is slow (A6U1-8), read and write accesses go to "attribute" memory on the card. Attribute memory is typically a small EEPROM on the memory card that contains special information that specifies the manufacturer of the card, type and size of memory on the card, memory speed, etc. When REG* is high, read and write accesses go to the "common" memory on the card. Common memory is the Static RAM on the memory cards used in this instrument.

Typically, information is read and written to the memory card in a sequential manner where the address counter automatically increments after the end of each read or write cycle. When the Memory Card Controller reads data from the memory card data bus (CD<0> through CD<7>), CE1* (A6U1-62) goes low followed by CRD* (A6U1-63) going low. The data from the memory card then goes through the Memory Card controller and is read by the Microprocessor on the D8 through D15 data bus lines.Data is written to the memory card in a similar manner, except that the data goes from the Microprocessor through the memory Card Controller and to the Memory Card with CWR* (A6U2-64) going low to enable the writing of the data to the memory. The purpose of A6U2 and resistors A6R2, A6R5, and A6R7 is to ensure that data on the Memory Card is not accidentally modified during the time that the instrument is being powered up or down. Each of the Memory Card data bus lines (CD<0> through CD<7>) has a series resistor (A6Z2) that helps ensure that the instrument meets EMI/EMC performance requirements.

The Memory Card Controller detects the insertion and removal of a Memory Card and interrupts the microprocessor by driving the MCINT* signal(A6U1-60) low. When a Memory Card is inserted in the PCMCIA Memory Card Connector, the CD1 (A6U1-19) and CD2 (A6U1-21) inputs on the Memory Card Controller are driven to 0V dc and Microprocessor (A1U1) is interrupted. The Microprocessor then powers up the Memory Card by setting A6U1-26 low, which turns on FET A6Q1 by driving the gate low through resistor A6R13. When FET A6Q1 is turned on the Memory Card power (CVCC and CVPP) is approximately +5.0V dc. When the Microprocessor has completed a data transfer with the Memory Card, FET A6Q1 is turned off again by driving A6U1-26 high.

When a Memory Card is inserted and powered up, the Memory Card outputs some status signals to the Memory Card Controller. If the Memory Card write protect switch is protecting data on the card, the WP signal (A6U1-22) is high. The status of the Memory Card battery is output on the BVD1 (A6P1-18) and BVD2 (A6P1-20) pins of the Memory Card Connector. If either of these battery status signals is low when the Memory Card is powered up, then the Microprocessor will turn on LED A6DS2 by driving A6U1-24 low. The Busy status LED (A6DS1) is turned on by driving A6U1-25 low when the Microprocessor has powered up the Memory Card and is transferring data to or from the card.

2A-74.PCMCIA Memory Card Connector

The PCMCIA Memory Card Connector (A6P1) is a 68 pin connector that meets the requirements of the Personal Computer Memory Card International Association. This connector has pins that are three different lengths: the card detection pins (CD1 and CD2) are the shortest, the power and ground pins are the longest, and the rest of the pins are a length in between. This ensures that on memory card insertion, the power and

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