For more information on the parts, including placement and pretty pictures, please see the assembly instructions.

ICs
IC1 & IC2		TC551001CP		128k x 8 static RAM		or any compatible SRAM
IC3		MAX232		RS232 serial interface
IC4		74LS33		Quad OC NOR
IC5		74LS393		Dual 4-bit counter
IC6		7805		5-volt voltage regulator
IC7		75452		OC Line driver		mistakenly labeled as 75453 in schematic
IC8		PIC16C65b		MicroChip PIC processor		can use the 16C74b as well
IC9		74LS00		Quad 2-input nand
Discrete
R1-R2, R9		10k ohm resistor		pull-ups
R3-R7		470 ohm resistor		LED drivers
R8,R10,R11		1k ohm resistor		drive-select pull-ups
C1-C4		10 uF electrolytic cap		MAX232 caps
C5-C6		47 uF electrolytic cap		power supply caps
C7		1 uF cap		noise filter cap
Other
LEDs (x5)		Minature LEDs				I used 3 green and 2 yellow
QG1		20 MHz Oscillator
Hardware
SV1		34-pin box header
X1		9-pin sub-D		female RS232 connector
JP3 & JP2		2-circuit pin header
- (2)		2-circuit connector
-		SPST Toggle		power switch
-		SPST Momentary Pushbutton		reset switch
-		Power Jack		2.5mm
case		Serpac 151				can use the 251 also

PCB Source Files

Eagle Source Files

Version 2.0 - Schematic File   (212 kB)
Version 2.0 - PCB (board)   (91 kB)

Version 2.0 - Printable Schematic   (813 kB)
Version 2.0 - PCB Parts Layout   (281 kB)

PCB Manufacturing Files (Gerbers)

Version 2.0 - Zip of all Gerbers   (57 kB)

The SVD is implemented using a PIC 16C65B. You can download the firmware here: PIC v2.3 firmware   (70 kB).

Firmware Files

There are 5 types of files in the firmware zip file as follows:

vd.mcp	The MicroChip IDE project file. You need to download the IDE to work with this file, though it isn't completely necessary if you have a compatible assembler. Note, however, that one include file "p16c74b.inc" (in vd.h) isn't included in this distribution as it is part of the MicroChip IDE.
linker.lkr	Definitions of the sections and code pages when assembling the code for the PIC. Pretty standard stuff. Originally a copy of one of the PIC linker files.
*.asm	all files ending with .asm - These are the main code files for the SVD firmware. Note, however, that much of the code doesn't reside in these files. Instead, many include .mac or "macro" files. Normally macro files are used when macros are used repeatedly throughout the code.
*.h	all files ending with .h - These files define basic parameters (like memory locations) and also define functions that will be called from other files.
*.mac	all files ending with .mac - These files have normal "code" but are defined as macros which are included throughout the .asm files. Often these macros are used repeatedly throughout the code. Though in some cases the macro was defined in preparation for repeated use, but may only be used once.

Firmware Notes

Overview	The firmware has two basic jobs: communication with the PC over the serial port, and pretending to be a floppy drive to the vintage computer. PC communication is accomplished through the PIC serial communication hardware, and is interrupt driven. Floppy emulation operations are not interrupt driven. Floppy emulation is sector driven. Each sector has a leading byte that dispatches to a routine that generates data in the format indicated for that sector. The one exception to this rule is the Apple NIB format which generates an entire track depending upon the format indicated for the first sector.
Code Comments	You will notice that within critical sections of the code the comments at the end of the line of code often has a number (positive or negative) within parenthesis after the semi-colon but before the actual comment. This number is a reminder of the instruction cycle count remaining (or until) the next pulse is scheduled to be generated. In most cases, the pulse/data cells are separated by 20 instruction cycles (4 us per cell). You should be able to see that "0" is reached when a pulse is generated.
Macros	Macros are liberally used throughout the code. Some of the more interesting and heavily used are: Raise/Lower When this project started, I didn't know what polarity the signals would end-up being - positive or negative logic. In portdef.h you will see that the signals can be easily defined with either positive or negative logic and that Raise and Lower cause the signal to go high or low in concert with the type of logic used. You will also notice that each signal ended up with negative logic...making this set of macros superfluous. WaitXX Where "XX" is one or two numerical digits. This macro is used EVERYWHERE, and causes a "wait" for the given number of instruction cycles. However, the wait will execute a HeadCheck (see below) as many times as possible while waiting. Note that different wait's are called depending upon which code page we are operating in. HeadCheck Checks to see if a head move is being requested by the driving vintage computer. The head move line is sampled, and if a head move is being requested, the code dispatches to the movement routine. When head movement occurs, all bets are off regarding the timing for the pulses...which is OK. As with WaitXX different HeadChecks are called depending upon the code page.
Code Pages	The code uses 2 pages of instruction memory on the PIC. It is split fairly evenly between the two, and great care is taken to make sure that the right calls are done in the right pages. Things do flip back and forth in the code as necessary.
Memory Interface	As you can see in the schematic, the lower 8 bits of memory are driven by a counter as opposed to the PIC. The PIC simply pulses the memory increment line to bump the lower 8 bits of the address. The upper bits of the address are separated into a hi-block and low-block address. Critical sections of the code assume that the low-block address can simply be incremented - the address will not roll-over requiring the hi-block address to be incremented. This behavior is ensured by picking the appropriate starting addresses for the blocks as well as accounting for appropriate increments and decrements when moving from track to track.
Serial Protocol	The serial.asm code implements a serial protocol for communicating with the PC. Details on this protocol can be found here.
Sector Size	Note that the code plans for different sector sizes. No sizes other than 256 are implemented currently.

Downloading SVD Building Instructions

When you order the SVD in "kit" form, it comes with an assembly manual.

You can also download the manual in a few forms:

Standard US Letter Size -	SVD-Instructions.pdf   (4,163 kB)
"Booklet" on US Letter Size -	SVD-Booklet-Front.pdf   (589 kB)
	SVD-Booklet-Back.pdf   (3,424 kB)