The IOP16 runs at 8 of 50 MHz clocks per instruction. That is 6.25 MIPS which really is way more than fast enough for this use. The states are Grey Coded as follows:

Most of the cycles do nothing. There is no good reason this can't run twice as fast. The Grey Codes are:

Made the change and it worked. It now runs at 12.5 MIPS. Way overkill, but why not.

The backspace key that the PDP-8 expects isn't the CTRL-H key (0x08 ASCII value) . The key needs to be mapped to ASCII 0x7F. Fortunately, the PS/2 keyboard VHDL code (ps2_keyboard_to_ascii.vhd) makes this easy to change. 

It works!

It's a great retro feeling to use the amber VDU screen and PS/2 keyboard built into the FPGA. However, sometimes I prefer to use PuTTY on the USB serial terminal, particularly when I want to capture screens. But the use of the serial source jumper does present the possibility of confusion to which port is being used (VDU or USB serial).

Added auto-detection of the Serial port source. If the serSelect jumper (J3-1) is installed the USB is used. The serSelect is routed to the IOP16 CPU and checked. If USB is selected, the VDU screen shows "USB" added to the banner. This is useful to let the user know that the VDU is not being used.

Output on PuTTY:

Added subroutines for UART and VDU initialization to the IOP16 code. Also, added an ANSI screen clear command (0x0c). Here's a handy ANSI codes chart.  

Here's the IOP16 code (latest version is here).

000    START   0xA017    JSR    INITVDU         INITIALIZE THE VDU    
001            0xA01C    JSR    INITURT         INITIALIZE THE ACIA UART    
002            0xA014    JSR    CLRSCR          CLEAR THE SCREEN CMD    
003    LOOP    0xA006    JSR    KB2PDP          KEYBOARD TO PDP-8    
004            0xA00D    JSR    PDP2VDU         PDP-8 TO VGA    
005            0xE003    JMP    LOOP            LOOP FOREVER    
006    KB2PDP  0x6004    IOR    Reg0    IO_04   READ KBD STATUS    
007            0x8001    ARI    Reg0    0X01    MASK RX DATA PRESENT BIT    
008            0xC004    BEZ    NOKDBD          NO KBD DATA    
009            0x6105    IOR    Reg1    IO_05   READ KBD DATA    
00a            0x9180    ORI    Reg1    0X80    MARK PARITY    
00b            0x7101    IOW    Reg1    IO_01   WRITE TO UART DATA    
00c    NOKDBD  0xB000    RTS                    DONE KEYBOARD TO UART    
00d    PDP2VDU 0x6000    IOR    Reg0    IO_00   PDP-11 TO VDU    
00e            0x8001    ARI    Reg0    0X01    MASK RX DATA PRESENT BIT    
00f            0xC004    BEZ    NOPDPD          NO UART DATA    
010            0x6101    IOR    Reg1    IO_01   READ UART DATA    
011            0x817F    ARI    Reg1    0X7F    8 TO 7 BITS    
012            0x7103    IOW    Reg1    IO_03   WRITE OUT SCREEN    
013    NOPDPD  0xB000    RTS            DONE    UART TO VGA    
014    CLRSCR  0x200C    LRI    Reg0    0X0C    SCREEN CLEAR    
015            0x7003    IOW    Reg0    IO_03   WRITE OUT SCREEN    
016            0xB000    RTS                            
017    INITVDU 0x2003    LRI    Reg0    0X03    RESET TERMINAL COMMAND    
018            0x7002    IOW    Reg0    IO_02   WRITE VDU CMD REG    
019            0x2020    LRI    Reg0    0X20    TX CTRLS RTS    
01a            0x7002    IOW    Reg0    IO_02   WRITE VDU CMD REG    
01b            0xB000    RTS                            
01c    INITURT 0x2003    LRI    Reg0    0X03    RESET UART COMMAND    
01d            0x7000    IOW    Reg0    IO_00   WRITE UART CMD REG    
01e            0x2020    LRI    Reg0    0X20    TX CTRLS RTS    
01f            0x7000    IOW    Reg0    IO_00   WRITE UART CMD REG    
020            0xB000    RTS                            

There was enough resources to put my ANSI Terminal into the FPGA. It displays on a VGA monitor and input comes from a PS/2 keyboard. The ANSI Terminal uses my IOP16 CPU. The terminal connects via an internal 9600 baud serial connection.

The IOP16 code is pretty simple. The only "tricky" part is adding MARK parity when sending serial data to the PDP-8 serial in and stripping off the MARK parity when sending the data out of the PDP-8 into the VDU. 

000            0x2003    LRI    Reg0    0X03    RESET TERMINAL COMMAND    
001            0x7002    IOW    Reg0    IO_02   WRITE VDU CMD REG    
002            0x2003    LRI    Reg0    0X03    RESET UART COMMAND    
003            0x7000    IOW    Reg0    IO_00   WRITE UART CMD REG    
004            0x2020    LRI    Reg0    0X20    TX CTRLS RTS    
005            0x7002    IOW    Reg0    IO_02   WRITE VDU CMD REG    
006            0x2020    LRI    Reg0    0X20    TX CTRLS RTS    
007            0x7000    IOW    Reg0    IO_00   WRITE UART CMD REG    
008   START    0xA00B    JSR    KB2PDP          KEYBOARD TO PDP-8    
009            0xA012    JSR    PDP2VDU         PDP-8 TO VGA    
00a            0xE008    JMP    START           LOOP FOREVER    
00b   KB2PDP   0x6004    IOR    Reg0    IO_04   READ KBD STATUS    
00c            0x8001    ARI    Reg0    0X01    MASK RX DATA PRESENT BIT    
00d            0xC004    BEZ    NOKDBD          NO KBD DATA    
00e            0x6005    IOR    Reg0    IO_05   READ KBD DATA    
00f            0x9080    ORI    Reg0    0X80    MARK PARITY    
010            0x7001    IOW    Reg0    IO_01   WRITE TO UART DATA    
011   NOKDBD   0xB000    RTS                    DONE KEYBOARD TO UART    
012   PDP2VDU  0x6000    IOR    Reg0    IO_00   PDP-11 TO VDU    
013            0x8001    ARI    Reg0    0X01    MASK RX DATA PRESENT BIT    
014            0xC004    BEZ    NOPDPD          NO UART DATA    
015            0x6001    IOR    Reg0    IO_01   READ UART DATA    
016            0x807F    ARI    Reg0    0X7F    8 TO 7 BITS    
017            0x7003    IOW    Reg0    IO_03   WRITE OUT SCREEN    
018   NOPDPD   0xB000    RTS                    DONE UART TO VGA    

Resources

GitHub repo is here.

It worked!

Uses most of the internal SRAM. Plenty of logic space left over:

Thought it might be a useful idea to have hardware handshake enabled.

In the top file CPU entity:

     -- TTY1 Interfaces
     tty1BR   => uartBR9600,                 --! TTY1 is 9600 Baud
     tty1HS   => uartHShw,                   --! TTY1 uses hardware handshake
     tty1CTS  => TTY1_CTS,                   --! TTY1 CTS (in)
     tty1RTS  => TTY1_RTS,                   --! TTY1 RTS (out)
     tty1RXD  => TTY1_RXD,                   --! TTY1 RXD (to RS-232 interface)
     tty1TXD  => TTY1_TXD,                   --! TTY1 TXD (to RS-232 interface)

From Doug Jones PDP-8 page. "From the beginning, PDP-8 software has generally assumed that textual I/O would be in 7 bit ASCII. Most early PDP-8 systems used teletypes as console terminals; as sold by DEC, these were configured for mark parity, so most older software assumes 7 bit ASCII, upper case only, with the 8th bit set to 1. "

In PuTTY:

Works!

Fresh Boot

• USB cable disconnected (FPGA card is off).
• Run/Halt on Front Panel set to HALT (down position).
• Set Address switches on Front Panel to 0023.
• Plug in USB cable to PC.
• PC LED on Front Panel should display next address (0024).
• Run PuTTY on PC.
• Serial port found in device Manager.
• Serial port set to 9600,SPACE,7,1 (may not be optimal but it worked).

• Turn on RUN switch on Front Panel.
• Press RES button on Front Panel.
• Prompt comes up in Serial terminal (PuTTY).

Reboot

The Internal SRAM needs to reloaded.

• Run/Halt on Front Panel to HALT (down position).
• Hit load switch on FPGA card (SW3).
• Turn on RUN switch on Front Panel.
• Press RES button on Front Panel.
• Prompt comes up in Serial terminal (PuTTY).

Alternate Re-boot

From the OS8 Handbook. Boots to command line.

• Set Run/Halt to HALT
• Set switches to 7600
• Press RES (Reset)
• Press LDPC (Load PC)
• Press RES (Reset)
• Set Run/Halt to RUN
• Press RES

Files on the RK08 (SD Card)

• DIR /A

ABSLDR.SV   6            FLOP2 .BI   2            RALF  .SV  19
ADVENT.DC   9            FORLIB.RL 170            REMEM .SV   5
ADVENT.FT  11            FOTP  .SV   8            RESORC.SV  14
ADVENT.IN   1            FRTS  .SV  26            RKBOOT.SV   2
ADVENT.LD 145            FUGUE .MU  42            RKCOPY.SV  11
ADVENT.RL   4            FUTIL .SV  27            RKFRMT.SV   9
ADVENT.TX 201            F4    .SV  20            RKUTIL.SV  15
AINDX .DA  50            GETIN .FT   6            RLFRMT.SV   7
AMAIN .RA 270            GETIN .RL   4            RL2FMT.SV   8
AMAIN .RL  50            GETWRD.RA  16            RND   .FT   1
ATEXT .DA 144            GETWRD.RL   2            RND   .RL   2
A5TOA1.RA   6            HEADER.SV  14            RSPEAK.RA   3
A5TOA1.RL   3            HELP  .HL 102            RSPEAK.RL   2
BASIC .AF   4            HELP  .SV   8            RSTRGM.FT  13
BASIC .BA  11            INIT  .TX   1            RSTRGM.RL   8
BASIC .FF   4            INITAD.FT  65            RTFLOP.SV  15
BASIC .OV  16            INITAD.RL  23            RUNAD .BI   1
BASIC .SF   4            INUSE .TE   8            RXCOPY.SV   9
BASIC .SV  11            IO    .FT   2            RXFIX .SV   3
BASIC .UF   2            IO    .RL   2            RXREAD.SV   7
BASIC .WS   1            JUGGLE.RA   3            SAVEGM.FT  13
BATCH .SV  10            JUGGLE.RL   2            SAVEGM.RL   8
BCOMP .SV  17            KL8E  .PA  53            SD    .BN   1
BITMAP.SV   5            K12DEB.SV   4            SD    .LS  28
BITSET.RA  11            K12DEC.SV   5            SD    .PA  11
BITSET.RL   3            K12DJG.SV  33            SEED  .RA   7
BLOAD .SV   8            K12ENB.SV   4            SEED  .RL   2
BLOCKS.SV   8            K12ENC.SV   6            SET   .SV  20
BOOK  .BI   1            K12MIT.SV  33            SPACWR.BA  39
BOOT  .SV   5            LAYOUT.TX   4            SPEAK .RA  28
BRTS  .SV  15            LCSYS .BI   3            SPEAK .RL   4
BUG   .FT   3            LOAD  .BI   1            SRCCOM.SV   5
BUG   .RL   2            LOAD  .LS   8            SVDUMP.SV   4
BUILD .SV  37            LOAD  .SV  16            TDCOPY.SV   7
CAMP  .SV  13            LPTSPL.SV  10            TDFRMT.SV   9
CARRY .RA   5            MCPIP .SV  13            TECKBM.TE   2
CARRY .RL   2            MOVE  .RA   4            TECO  .IN   1
CCL   .SV  31            MOVE  .RL   2            TECO  .SV  32
CHESS .SV  15            MSBAT .SV  23            TECO  .TE   1
COMPAF.SV   5            MUSIC .SV   9            UCSYS .BI   3
COMPIL.BI   2            PAL8  .SV  19            USR   .RA  46
CONVRT.SV   5            PARAM .SV  12            USR   .RL   4
CREF  .SV  13            PASS2 .SV  20            VOCAB .RA   7
DECX8 .SV  43            PASS2O.SV   5            VOCAB .RL   3
DIRECT.SV   7            PASS3 .SV   8            VTEDIT.TE   8
DOUGTE.ST   1            PCT   .RA   2            WILD  .BI   1
DROP  .RA   4            PCT   .RL   2            WILD  .DI   5
DROP  .RL   2            PIP   .SV  11            WILD  .TE   2
DSTROY.RA   1            PIP10 .SV  17            WILD  .TM   1
DSTROY.RL   2            PSPEAK.RA   5            WPFLOP.SV  14
DTCOPY.SV   5            PSPEAK.RL   2            YES   .FT   2
DTFRMT.SV   7            PUT   .RA   3            YES   .RL   3
EDIT  .SV  10            PUT   .RL   2            2000  .TX   1
EPIC  .SV  14            QUIT  .SV   2            31    .76   1
FLOP  .HN   3

 Resources

.R RESORC
*/E

163 FILES IN 2639 BLOCKS USING 5 SEGMENTS
553 FREE BLOCKS (7 EMPTIES)

#  NAME TYPE MODE SIZ BLK KIND U V ENT USER
01 SYS  RK8E RWF 3248 SYS      0 F  07
02 DSK  RK8E RWF 3248 SYS      0 F  07
03 BAT  BAT  R        16         B  00
04 TTY  TTY  RW       17+ KL8E   E 176
05 RKA0 RK8E RWF 3248 20  RK05 0 A  20
06 RKB0 RK8E RWF 3248 20  RK05 0 A  21
07 RKA1 RK8E RWF 3248 20  RK05 1 A  22
10 RKB1 RK8E RWF 3248 20  RK05 1 A  23
11 RKA2 RK8E RWF 3248 20  RK05 2 A  24
12 RKB2 RK8E RWF 3248 20  RK05 2 A  25
13 RXA0 RX02 RWF  988 21+           32
14 RXA1 RX02 RWF  988 21+           36
15 B3    37  RWF      22+          117
16 B4    37  RWF      22+          113

FREE DEVICE SLOTS: 01,  FREE BLOCK SLOTS: 03
OS/8 V3T

Running VirtualBox under Windoze. Transferring files between Windoze and Linux via GitHub.

Combined the 4 images inspired by Startup page:  

• http://www.pdp8online.com/ftp/images/os8/multos8.rk05
• http://www.pdp8online.com/ftp/images/os8/diag-games-kermit.rk05
• http://www.pdp8online.com/ftp/images/os8/diagpack2.rk05
• http://www.rickmurphy.net/advent/advent.rk05

Created single image.

Burned to blank SD card using Balena Etcher.

OS/8 Boots:

Set serial port configuration: