SECTION 5

RAM OVERLAY

5-1	Overview
5-2	Installation
5-3	Controls
5-4	Uploading/Downloading

5-1 OVERVIEW

The emulator may be equipped with an optional RAM overlay feature. Either 8K bytes of 200 nS static RAM, or 16K or 64K bytes of 150 nS static RAM are available on a circuit board which includes the appropriate addressing and buffering.

The 8K-byte memory is divided into two independet 4K-byte memory banks. Each bank has independent control circuitry and mey be enabled as read/write memory, read only memory, or disabled. Each 4K bank may be independently set to occupy a specific address range.

The 16K-byte memory is also divided into two independent 8K-byte memory banks. Each bank has independent control circuitry and mey be enabled as read/write memory, read only memory, or disabled. Each 8K bank is further divided into two 4K blocks that can each be independently set to occupy a specific address range. If only a single 4K block is required, set both blocks to the same address range.

The 64K-byte memory is divided into sixteen 4K-byte memory banks that can overlay the entire memory space. Each bank may be enabled as read/write memory, read only memory, or disabled by one of the sixteen switches. The address fo reach 4K is hardwired so that it is only necessary to enable those banks that are needed. Refer to Figure 5-1.1.

Cut here and remove

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a.) 8K and 16K RAM Overlays

Figure 5-1.1 RAM Overlay Decals

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b.) 64K RAM Overlay

5-2 INSTALLATION

To install a RAM Overlay option in your emulator (units wtihotu the two hex stand-offs, as shown in Figure 5-2.1), the procedure is as follows:

1.	Unplug the power cord from the back of the emulator.
2.	Unplug the pod cables attached to the back of the emulator, noting the proper positioning.
3.	Turn the emulator upside-down and place it on a soft surface to prevent scratching the top cover.
4.	Remove the four top cover securing screws and the four rubber feet from the bottom of the emulator.
5.	Remove the bottom cover.
6.	Turn the emulator upright and carefully remove the topcover.
7.	Remove the four display assembly securing screws, being careful not to scratch the display plex panel. Note the location of the spacers behind the plex panel.
8.	Remove the display assembly.
9.	Remove the four keyboard assembly securing screws.
10.	Remove the keyboard assembly.
11.	Unplug the four-contact Molex connector from the power supply regulator board, located next to the power switch.
12.	Remove the two securing screws located on either side of the pod cable connector at the rear of the unit.
13.	Slide the main logic assembly forward and out of the emulator frame. Note that it is necessary to install the new mounting bracket included in your 64K RAM kit onto the Main Logic Board.
14.	Install the two hex standoffs supplied into the position shown in Figure 5-2.1. The standoffs will be secured into place by using two screws supplied in the installation kit. (Install the screws from the bottom side of the assembly).
15.	Cut the lower half of the back panel decal to expose the cutouts as shown in Figure 5-1.1a for the 8K and 16K RAM Overlays only. For the 64K RAM Overlay, remove the old decal and replace it with the new one supplied in your 64K RAM Kit.
16.	Plug the RAM Overlay connector into the main logic assembly.
17.	Reassemble the emulator by reversing steps 1 through 13.
18.	Connect the probe tip assembly to a known-good target system.

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Figure 5-2.1 RAM Overlay Installation

If a RAM Overlay block is set up to respond to a range of addresses, say 0000₁₆ to 0FFF₁₆, then target system memory in the same address range becomes inaccessible to the emulation processor. The memory block has "overlayed" the corresponding target system addresses. (See, however, the description of Code Function C5 for an exception to this characteristic of the emulator.)

The contents of the RAM Overlay are retained as long as power is applied to the emulator. It is possible to load the RAM Overlay with data, turn the enable switches off and retrieve the data at a later time. To retrieve data, turn the enable switches to either the READ or RD/WR position.

Each 4K byte block of memory for 8K and 16K RAM Overlays has an associated Address Range switch. The 64K RAM Overlay also has an associated control switch for each 4K block of memory. See Figure 5-3.1.

5-3 CONTROLS

The enable switches are three-position toggle switches that place the memory bank into one of three conditions:

•	OFF
	The memory bank is disabled and is effectively removed from the system.
•	Read
	The memory bank is placed in a Read/Only configuration so that from the point of view of the target system the memory bank behaves like memory.
•	Read/Only
	In this mode, it is not possible for the target system program to alter the contents of the memory. Note, however, that the emulator is still able to write to the memory bank from the keyboard or from a Code Function routine such as Code Function C3 (download).
•	Read/Write
	The memory bank is placed in a Read/Write configuration. Both the target system and the emulator are able to read the memory and write new information to it.

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a) 8K

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b) 16K

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c) 64K

Figure 5-3.1
RAM Overlay Controls

If a memory bank is disabled (toggle switch in the off position), the memory wil nevertheless continue to retain data. The data will reappear in the target address space whenever the memory is again enabled.

The address range switches for the 8K and 16K RAM Overlays are 16-position rotary switches used to select the address range where the 4K memory blocks will reside in the target address space. Each of the 4K memory blocks can be moved to any of 16 positions, beginning at a 4K boundary. See Table 5-1.

TABLE 5-1 MEMORY BLOCK ADDRESSES A and B

SWITCH	MEMORY BLOCK	SWITCH	MEMORY BLOCK
POSITION	ADDRESS	POSITION	ADDRESS

0	0000₁₆-0FFF₁₆	8	8000₁₆-8FFF₁₆
1	1000₁₆-1FFF₁₆	9	9000₁₆-9FFF₁₆
2	2000₁₆-2FFF₁₆	A	A000₁₆-AFFF₁₆
3	3000₁₆-3FFF₁₆	B	B000₁₆-BFFF₁₆
4	4000₁₆-4FFF₁₆	C	C000₁₆-CFFF₁₆
5	5000₁₆-5FFF₁₆	D	D000₁₆-DFFF₁₆
6	6000₁₆-6FFF₁₆	E	E000₁₆-EFFF₁₆
7	7000₁₆-7FFF₁₆	F	F000₁₆-FFFF₁₆

Because of the large memory capacity, the card setup for the 64K RAM is slightly different than the 8K and the 16K RAM. The memory control switches onsist of sixteen three-position switches. Eighteen switches are present, however two are not used. Each switch represents a 4K byte segment of memory. The switch in the up position enables the RD/WR emmory; in the down position enables the RD only memory; and ithe center position disables the memory. The decal on the back of the EM dwnotes the switch positions and memory range.

5-4 UPLOADING/DOWNLOADING

Programs can be transferred to the RAM Overlay from the target system, the front panel EPROM socket or the RS-232C serial port on the auxillary connector. Programs in the RAM Overlay can be dumped to the RS-232C port. Both uploading and downloading is accomplished by enabling the RAM Overlay for read only or read/write, selecting the desired address range via the rotary switches, and then executing the appropriate Code Functions C1 through C6. A summary of these Code Functions is given below. (For more information see Sec. 7, Built-in Diagnostic Functions.) Note that the overlay block involved must be enabled; otherwise, these code functions will involve the target system memory in place of the RAM Overlay.

CODE C1—LOAD RAM OVERLAY FROM FRONT PANEL PROM

This Code Function transfers data from the front panel diagnostic EPROM to the Overlay RAM. To use this Code Function, first enter the starting and ending address values in the BEG and END registers, then start the routine.

CODE C2—VERIFY RAM OVERLAY AGAINST FRONT PANEL PROM

Code C2 compares the front panel PROM with the address range specified by the user. The address range is loaded into the BEG and END register. If a non-verify occurs, the Diagnostic Emulator emits three beeps and pauses. The address and the data that failed to verify are shown on the display. By depressing and holding the EXAM keyswitch, the correct data will be displayed.

CODE C3—LOAD RAM OVERLAY FROM SERIAL LINK

Code C3 transfers hex data from the RS-232C input to the RAM Overlay. To use this Code Function, connect the RS-232C input to the source of informat, start the routine, and then enable the source to download the appropriate data.

CODE C4—DUMP RAM OVERLAY TO SERIAL LINK

Code C4 transfers data from selected areas of RAM Overlay to the serial RS-232C output. To use the Code Function, first specify the address limits in the BEG and END registers, next prepare the receiving device to accept data, then start the routine.

CODE C5—LOAD RAM OVERLAY FROM TARGET MEMORY

Code C5 transfers data from selected areas of target memory space to the equivalent areas in Overlay Memory. The BEG and END registers are set to the range of addresses from which data is to be transferred.

CODE C6—VERIFY RAM OVERLAY WITH TARGET MEMORY

Code C6 compares data from selected areas of target program memory to the equivalent areas in Overlay Memory. The BEG and END registers are set to the desired target memory address range.

If a non-verify occurs, the Diagnostic Emulator emits three beeps and pauses. The address and the data that failed to verify are shown on the display, by depressing and holding the EXAM Keyswitch, the correct data will be displayed.